[PATCH v4 4/4] RISC-V: Add arch functions to support hibernation/suspend-to-disk

[Alexandre Ghiti]

On 2/27/23 04:11, JeeHeng Sia wrote:
>
>> -----Original Message-----
>> From: Alexandre Ghiti <alex at ghiti.fr>
>> Sent: Friday, 24 February, 2023 8:29 PM
>> To: JeeHeng Sia <jeeheng.sia at starfivetech.com>; paul.walmsley at sifive.com; palmer at dabbelt.com; aou at eecs.berkeley.edu
>> Cc: linux-riscv at lists.infradead.org; linux-kernel at vger.kernel.org; Leyfoon Tan <leyfoon.tan at starfivetech.com>; Mason Huo
>> <mason.huo at starfivetech.com>
>> Subject: Re: [PATCH v4 4/4] RISC-V: Add arch functions to support hibernation/suspend-to-disk
>>
>> On 2/21/23 03:35, Sia Jee Heng wrote:
>>> Low level Arch functions were created to support hibernation.
>>> swsusp_arch_suspend() relies code from __cpu_suspend_enter() to write
>>> cpu state onto the stack, then calling swsusp_save() to save the memory
>>> image.
>>>
>>> Arch specific hibernation header is implemented and is utilized by the
>>> arch_hibernation_header_restore() and arch_hibernation_header_save()
>>> functions. The arch specific hibernation header consists of satp, hartid,
>>> and the cpu_resume address. The kernel built version is also need to be
>>> saved into the hibernation image header to making sure only the same
>>> kernel is restore when resume.
>>>
>>> swsusp_arch_resume() creates a temporary page table that covering only
>>> the linear map. It copies the restore code to a 'safe' page, then start
>>> to restore the memory image. Once completed, it restores the original
>>> kernel's page table. It then calls into __hibernate_cpu_resume()
>>> to restore the CPU context. Finally, it follows the normal hibernation
>>> path back to the hibernation core.
>>>
>>> To enable hibernation/suspend to disk into RISCV, the below config
>>> need to be enabled:
>>> - CONFIG_ARCH_HIBERNATION_HEADER
>>> - CONFIG_ARCH_HIBERNATION_POSSIBLE
>>>
>>> Signed-off-by: Sia Jee Heng <jeeheng.sia at starfivetech.com>
>>> Reviewed-by: Ley Foon Tan <leyfoon.tan at starfivetech.com>
>>> Reviewed-by: Mason Huo <mason.huo at starfivetech.com>
>>> ---
>>>    arch/riscv/Kconfig                 |   7 +
>>>    arch/riscv/include/asm/assembler.h |  20 ++
>>>    arch/riscv/include/asm/suspend.h   |  19 ++
>>>    arch/riscv/kernel/Makefile         |   1 +
>>>    arch/riscv/kernel/asm-offsets.c    |   5 +
>>>    arch/riscv/kernel/hibernate-asm.S  |  77 +++++
>>>    arch/riscv/kernel/hibernate.c      | 447 +++++++++++++++++++++++++++++
>>>    7 files changed, 576 insertions(+)
>>>    create mode 100644 arch/riscv/kernel/hibernate-asm.S
>>>    create mode 100644 arch/riscv/kernel/hibernate.c
>>>
>>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>>> index e2b656043abf..4555848a817f 100644
>>> --- a/arch/riscv/Kconfig
>>> +++ b/arch/riscv/Kconfig
>>> @@ -690,6 +690,13 @@ menu "Power management options"
>>>
>>>    source "kernel/power/Kconfig"
>>>
>>> +config ARCH_HIBERNATION_POSSIBLE
>>> +	def_bool y
>>> +
>>> +config ARCH_HIBERNATION_HEADER
>>> +	def_bool y
>>> +	depends on HIBERNATION
>>> +
>>>    endmenu # "Power management options"
>>>
>>>    menu "CPU Power Management"
>>> diff --git a/arch/riscv/include/asm/assembler.h b/arch/riscv/include/asm/assembler.h
>>> index 727a97735493..68c46c0e0ea8 100644
>>> --- a/arch/riscv/include/asm/assembler.h
>>> +++ b/arch/riscv/include/asm/assembler.h
>>> @@ -59,4 +59,24 @@
>>>    		REG_L	s11, (SUSPEND_CONTEXT_REGS + PT_S11)(a0)
>>>    	.endm
>>>
>>> +/*
>>> + * copy_page - copy 1 page (4KB) of data from source to destination
>>> + * @a0 - destination
>>> + * @a1 - source
>>> + */
>>> +	.macro	copy_page a0, a1
>>> +		lui	a2, 0x1
>>> +		add	a2, a2, a0
>>> +1 :
>>> +		REG_L	t0, 0(a1)
>>> +		REG_L	t1, SZREG(a1)
>>> +
>>> +		REG_S	t0, 0(a0)
>>> +		REG_S	t1, SZREG(a0)
>>> +
>>> +		addi	a0, a0, 2 * SZREG
>>> +		addi	a1, a1, 2 * SZREG
>>> +		bne	a2, a0, 1b
>>> +	.endm
>>> +
>>>    #endif	/* __ASM_ASSEMBLER_H */
>>> diff --git a/arch/riscv/include/asm/suspend.h b/arch/riscv/include/asm/suspend.h
>>> index 75419c5ca272..3362da56a9d8 100644
>>> --- a/arch/riscv/include/asm/suspend.h
>>> +++ b/arch/riscv/include/asm/suspend.h
>>> @@ -21,6 +21,11 @@ struct suspend_context {
>>>    #endif
>>>    };
>>>
>>> +/*
>>> + * Used by hibernation core and cleared during resume sequence
>>> + */
>>> +extern int in_suspend;
>>> +
>>>    /* Low-level CPU suspend entry function */
>>>    int __cpu_suspend_enter(struct suspend_context *context);
>>>
>>> @@ -36,4 +41,18 @@ int __cpu_resume_enter(unsigned long hartid, unsigned long context);
>>>    /* Used to save and restore the csr */
>>>    void suspend_save_csrs(struct suspend_context *context);
>>>    void suspend_restore_csrs(struct suspend_context *context);
>>> +
>>> +/* Low-level API to support hibernation */
>>> +int swsusp_arch_suspend(void);
>>> +int swsusp_arch_resume(void);
>>> +int arch_hibernation_header_save(void *addr, unsigned int max_size);
>>> +int arch_hibernation_header_restore(void *addr);
>>> +int __hibernate_cpu_resume(void);
>>> +
>>> +/* Used to resume on the CPU we hibernated on */
>>> +int hibernate_resume_nonboot_cpu_disable(void);
>>> +
>>> +asmlinkage void hibernate_restore_image(unsigned long resume_satp, unsigned long satp_temp,
>>> +					unsigned long cpu_resume);
>>> +asmlinkage int hibernate_core_restore_code(void);
>>>    #endif
>>> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
>>> index 4cf303a779ab..daab341d55e4 100644
>>> --- a/arch/riscv/kernel/Makefile
>>> +++ b/arch/riscv/kernel/Makefile
>>> @@ -64,6 +64,7 @@ obj-$(CONFIG_MODULES)		+= module.o
>>>    obj-$(CONFIG_MODULE_SECTIONS)	+= module-sections.o
>>>
>>>    obj-$(CONFIG_CPU_PM)		+= suspend_entry.o suspend.o
>>> +obj-$(CONFIG_HIBERNATION)	+= hibernate.o hibernate-asm.o
>>>
>>>    obj-$(CONFIG_FUNCTION_TRACER)	+= mcount.o ftrace.o
>>>    obj-$(CONFIG_DYNAMIC_FTRACE)	+= mcount-dyn.o
>>> diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
>>> index df9444397908..d6a75aac1d27 100644
>>> --- a/arch/riscv/kernel/asm-offsets.c
>>> +++ b/arch/riscv/kernel/asm-offsets.c
>>> @@ -9,6 +9,7 @@
>>>    #include <linux/kbuild.h>
>>>    #include <linux/mm.h>
>>>    #include <linux/sched.h>
>>> +#include <linux/suspend.h>
>>>    #include <asm/kvm_host.h>
>>>    #include <asm/thread_info.h>
>>>    #include <asm/ptrace.h>
>>> @@ -116,6 +117,10 @@ void asm_offsets(void)
>>>
>>>    	OFFSET(SUSPEND_CONTEXT_REGS, suspend_context, regs);
>>>
>>> +	OFFSET(HIBERN_PBE_ADDR, pbe, address);
>>> +	OFFSET(HIBERN_PBE_ORIG, pbe, orig_address);
>>> +	OFFSET(HIBERN_PBE_NEXT, pbe, next);
>>> +
>>>    	OFFSET(KVM_ARCH_GUEST_ZERO, kvm_vcpu_arch, guest_context.zero);
>>>    	OFFSET(KVM_ARCH_GUEST_RA, kvm_vcpu_arch, guest_context.ra);
>>>    	OFFSET(KVM_ARCH_GUEST_SP, kvm_vcpu_arch, guest_context.sp);
>>> diff --git a/arch/riscv/kernel/hibernate-asm.S b/arch/riscv/kernel/hibernate-asm.S
>>> new file mode 100644
>>> index 000000000000..846affe4dced
>>> --- /dev/null
>>> +++ b/arch/riscv/kernel/hibernate-asm.S
>>> @@ -0,0 +1,77 @@
>>> +/* SPDX-License-Identifier: GPL-2.0-only */
>>> +/*
>>> + * Hibernation low level support for RISCV.
>>> + *
>>> + * Copyright (C) 2023 StarFive Technology Co., Ltd.
>>> + *
>>> + * Author: Jee Heng Sia <jeeheng.sia at starfivetech.com>
>>> + */
>>> +
>>> +#include <asm/asm.h>
>>> +#include <asm/asm-offsets.h>
>>> +#include <asm/assembler.h>
>>> +#include <asm/csr.h>
>>> +
>>> +#include <linux/linkage.h>
>>> +
>>> +/*
>>> + * int __hibernate_cpu_resume(void)
>>> + * Switch back to the hibernated image's page table prior to restoring the CPU
>>> + * context.
>>> + *
>>> + * Always returns 0
>>> + */
>>> +ENTRY(__hibernate_cpu_resume)
>>> +	/* switch to hibernated image's page table. */
>>> +	csrw CSR_SATP, s0
>>> +	sfence.vma
>>> +
>>> +	REG_L	a0, hibernate_cpu_context
>>> +
>>> +	restore_csr
>>> +	restore_reg
>>> +
>>> +	/* Return zero value. */
>>> +	add	a0, zero, zero
>>> +
>>> +	ret
>>> +END(__hibernate_cpu_resume)
>>> +
>>> +/*
>>> + * Prepare to restore the image.
>>> + * a0: satp of saved page tables.
>>> + * a1: satp of temporary page tables.
>>> + * a2: cpu_resume.
>>> + */
>>> +ENTRY(hibernate_restore_image)
>>> +	mv	s0, a0
>>> +	mv	s1, a1
>>> +	mv	s2, a2
>>> +	REG_L	s4, restore_pblist
>>> +	REG_L	a1, relocated_restore_code
>>> +
>>> +	jalr	a1
>>> +END(hibernate_restore_image)
>>> +
>>> +/*
>>> + * The below code will be executed from a 'safe' page.
>>> + * It first switches to the temporary page table, then starts to copy the pages
>>> + * back to the original memory location. Finally, it jumps to __hibernate_cpu_resume()
>>> + * to restore the CPU context.
>>> + */
>>> +ENTRY(hibernate_core_restore_code)
>>> +	/* switch to temp page table. */
>>> +	csrw satp, s1
>>> +	sfence.vma
>>> +.Lcopy:
>>> +	/* The below code will restore the hibernated image. */
>>> +	REG_L	a1, HIBERN_PBE_ADDR(s4)
>>> +	REG_L	a0, HIBERN_PBE_ORIG(s4)
>>> +
>>> +	copy_page a0, a1
>>> +
>>> +	REG_L	s4, HIBERN_PBE_NEXT(s4)
>>> +	bnez	s4, .Lcopy
>>> +
>>> +	jalr	s2
>>> +END(hibernate_core_restore_code)
>>> diff --git a/arch/riscv/kernel/hibernate.c b/arch/riscv/kernel/hibernate.c
>>> new file mode 100644
>>> index 000000000000..46a2f470db6e
>>> --- /dev/null
>>> +++ b/arch/riscv/kernel/hibernate.c
>>> @@ -0,0 +1,447 @@
>>> +// SPDX-License-Identifier: GPL-2.0-only
>>> +/*
>>> + * Hibernation support for RISCV
>>> + *
>>> + * Copyright (C) 2023 StarFive Technology Co., Ltd.
>>> + *
>>> + * Author: Jee Heng Sia <jeeheng.sia at starfivetech.com>
>>> + */
>>> +
>>> +#include <asm/barrier.h>
>>> +#include <asm/cacheflush.h>
>>> +#include <asm/mmu_context.h>
>>> +#include <asm/page.h>
>>> +#include <asm/pgalloc.h>
>>> +#include <asm/pgtable.h>
>>> +#include <asm/sections.h>
>>> +#include <asm/set_memory.h>
>>> +#include <asm/smp.h>
>>> +#include <asm/suspend.h>
>>> +
>>> +#include <linux/cpu.h>
>>> +#include <linux/memblock.h>
>>> +#include <linux/pm.h>
>>> +#include <linux/sched.h>
>>> +#include <linux/suspend.h>
>>> +#include <linux/utsname.h>
>>> +
>>> +/* The logical cpu number we should resume on, initialised to a non-cpu number. */
>>> +static int sleep_cpu = -EINVAL;
>>> +
>>> +/* Pointer to the temporary resume page table. */
>>> +static pgd_t *resume_pg_dir;
>>> +
>>> +/* CPU context to be saved. */
>>> +struct suspend_context *hibernate_cpu_context;
>>> +EXPORT_SYMBOL_GPL(hibernate_cpu_context);
>>> +
>>> +unsigned long relocated_restore_code;
>>> +EXPORT_SYMBOL_GPL(relocated_restore_code);
>>> +
>>> +/**
>>> + * struct arch_hibernate_hdr_invariants - container to store kernel build version.
>>> + * @uts_version: to save the build number and date so that the we do not resume with
>>> + *		a different kernel.
>>> + */
>>> +struct arch_hibernate_hdr_invariants {
>>> +	char		uts_version[__NEW_UTS_LEN + 1];
>>> +};
>>> +
>>> +/**
>>> + * struct arch_hibernate_hdr - helper parameters that help us to restore the image.
>>> + * @invariants: container to store kernel build version.
>>> + * @hartid: to make sure same boot_cpu executes the hibernate/restore code.
>>> + * @saved_satp: original page table used by the hibernated image.
>>> + * @restore_cpu_addr: the kernel's image address to restore the CPU context.
>>> + */
>>> +static struct arch_hibernate_hdr {
>>> +	struct arch_hibernate_hdr_invariants invariants;
>>> +	unsigned long	hartid;
>>> +	unsigned long	saved_satp;
>>> +	unsigned long	restore_cpu_addr;
>>> +} resume_hdr;
>>> +
>>> +static inline void arch_hdr_invariants(struct arch_hibernate_hdr_invariants *i)
>>> +{
>>> +	memset(i, 0, sizeof(*i));
>>> +	memcpy(i->uts_version, init_utsname()->version, sizeof(i->uts_version));
>>> +}
>>> +
>>> +/*
>>> + * Check if the given pfn is in the 'nosave' section.
>>> + */
>>> +int pfn_is_nosave(unsigned long pfn)
>>> +{
>>> +	unsigned long nosave_begin_pfn = sym_to_pfn(&__nosave_begin);
>>> +	unsigned long nosave_end_pfn = sym_to_pfn(&__nosave_end - 1);
>>> +
>>> +	return ((pfn >= nosave_begin_pfn) && (pfn <= nosave_end_pfn));
>>> +}
>>> +
>>> +void notrace save_processor_state(void)
>>> +{
>>> +	WARN_ON(num_online_cpus() != 1);
>>> +}
>>> +
>>> +void notrace restore_processor_state(void)
>>> +{
>>> +}
>>> +
>>> +/*
>>> + * Helper parameters need to be saved to the hibernation image header.
>>> + */
>>> +int arch_hibernation_header_save(void *addr, unsigned int max_size)
>>> +{
>>> +	struct arch_hibernate_hdr *hdr = addr;
>>> +
>>> +	if (max_size < sizeof(*hdr))
>>> +		return -EOVERFLOW;
>>> +
>>> +	arch_hdr_invariants(&hdr->invariants);
>>> +
>>> +	hdr->hartid = cpuid_to_hartid_map(sleep_cpu);
>>> +	hdr->saved_satp = csr_read(CSR_SATP);
>>> +	hdr->restore_cpu_addr = (unsigned long)__hibernate_cpu_resume;
>>> +
>>> +	return 0;
>>> +}
>>> +EXPORT_SYMBOL_GPL(arch_hibernation_header_save);
>>> +
>>> +/*
>>> + * Retrieve the helper parameters from the hibernation image header.
>>> + */
>>> +int arch_hibernation_header_restore(void *addr)
>>> +{
>>> +	struct arch_hibernate_hdr_invariants invariants;
>>> +	struct arch_hibernate_hdr *hdr = addr;
>>> +	int ret = 0;
>>> +
>>> +	arch_hdr_invariants(&invariants);
>>> +
>>> +	if (memcmp(&hdr->invariants, &invariants, sizeof(invariants))) {
>>> +		pr_crit("Hibernate image not generated by this kernel!\n");
>>> +		return -EINVAL;
>>> +	}
>>> +
>>> +	sleep_cpu = riscv_hartid_to_cpuid(hdr->hartid);
>>> +	if (sleep_cpu < 0) {
>>> +		pr_crit("Hibernated on a CPU not known to this kernel!\n");
>>> +		sleep_cpu = -EINVAL;
>>> +		return -EINVAL;
>>> +	}
>>> +
>>> +#ifdef CONFIG_SMP
>>> +	ret = bringup_hibernate_cpu(sleep_cpu);
>>> +	if (ret) {
>>> +		sleep_cpu = -EINVAL;
>>> +		return ret;
>>> +	}
>>> +#endif
>>> +	resume_hdr = *hdr;
>>> +
>>> +	return ret;
>>> +}
>>> +EXPORT_SYMBOL_GPL(arch_hibernation_header_restore);
>>> +
>>> +int swsusp_arch_suspend(void)
>>> +{
>>> +	int ret = 0;
>>> +
>>> +	if (__cpu_suspend_enter(hibernate_cpu_context)) {
>>> +		sleep_cpu = smp_processor_id();
>>> +		suspend_save_csrs(hibernate_cpu_context);
>>> +		ret = swsusp_save();
>>> +	} else {
>>> +		suspend_restore_csrs(hibernate_cpu_context);
>>> +		flush_tlb_all();
>>> +		flush_icache_all();
>>> +
>>> +		/*
>>> +		 * Tell the hibernation core that we've just restored the memory.
>>> +		 */
>>> +		in_suspend = 0;
>>> +		sleep_cpu = -EINVAL;
>>> +	}
>>> +
>>> +	return ret;
>>> +}
>>> +
>>> +static unsigned long _temp_pgtable_map_pte(pte_t *dst_ptep, pte_t *src_ptep,
>>> +					   unsigned long addr, pgprot_t prot)
>>> +{
>>> +	pte_t pte = READ_ONCE(*src_ptep);
>>> +
>>> +	if (pte_present(pte))
>>> +		set_pte(dst_ptep, __pte(pte_val(pte) | pgprot_val(prot)));
>>> +
>>> +	return 0;
>>> +}
>>
>> I don't see the need for this function
> Sure, can remove it.
>>
>>> +
>>> +static unsigned long temp_pgtable_map_pte(pmd_t *dst_pmdp, pmd_t *src_pmdp,
>>> +					  unsigned long start, unsigned long end,
>>> +					  pgprot_t prot)
>>> +{
>>> +	unsigned long addr = start;
>>> +	pte_t *src_ptep;
>>> +	pte_t *dst_ptep;
>>> +
>>> +	if (pmd_none(READ_ONCE(*dst_pmdp))) {
>>> +		dst_ptep = (pte_t *)get_safe_page(GFP_ATOMIC);
>>> +		if (!dst_ptep)
>>> +			return -ENOMEM;
>>> +
>>> +		pmd_populate_kernel(NULL, dst_pmdp, dst_ptep);
>>> +	}
>>> +
>>> +	dst_ptep = pte_offset_kernel(dst_pmdp, start);
>>> +	src_ptep = pte_offset_kernel(src_pmdp, start);
>>> +
>>> +	do {
>>> +		_temp_pgtable_map_pte(dst_ptep, src_ptep, addr, prot);
>>> +	} while (dst_ptep++, src_ptep++, addr += PAGE_SIZE, addr < end);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static unsigned long temp_pgtable_map_pmd(pud_t *dst_pudp, pud_t *src_pudp,
>>> +					  unsigned long start, unsigned long end,
>>> +					  pgprot_t prot)
>>> +{
>>> +	unsigned long addr = start;
>>> +	unsigned long next;
>>> +	unsigned long ret;
>>> +	pmd_t *src_pmdp;
>>> +	pmd_t *dst_pmdp;
>>> +
>>> +	if (pud_none(READ_ONCE(*dst_pudp))) {
>>> +		dst_pmdp = (pmd_t *)get_safe_page(GFP_ATOMIC);
>>> +		if (!dst_pmdp)
>>> +			return -ENOMEM;
>>> +
>>> +		pud_populate(NULL, dst_pudp, dst_pmdp);
>>> +	}
>>> +
>>> +	dst_pmdp = pmd_offset(dst_pudp, start);
>>> +	src_pmdp = pmd_offset(src_pudp, start);
>>> +
>>> +	do {
>>> +		pmd_t pmd = READ_ONCE(*src_pmdp);
>>> +
>>> +		next = pmd_addr_end(addr, end);
>>> +
>>> +		if (pmd_none(pmd))
>>> +			continue;
>>> +
>>> +		if (pmd_leaf(pmd)) {
>>> +			set_pmd(dst_pmdp, __pmd(pmd_val(pmd) | pgprot_val(prot)));
>>> +		} else {
>>> +			ret = temp_pgtable_map_pte(dst_pmdp, src_pmdp, addr, next, prot);
>>> +			if (ret)
>>> +				return -ENOMEM;
>>> +		}
>>> +	} while (dst_pmdp++, src_pmdp++, addr = next, addr != end);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static unsigned long temp_pgtable_map_pud(p4d_t *dst_p4dp, p4d_t *src_p4dp,
>>> +					  unsigned long start,
>>> +					  unsigned long end, pgprot_t prot)
>>> +{
>>> +	unsigned long addr = start;
>>> +	unsigned long next;
>>> +	unsigned long ret;
>>> +	pud_t *dst_pudp;
>>> +	pud_t *src_pudp;
>>> +
>>> +	if (p4d_none(READ_ONCE(*dst_p4dp))) {
>>> +		dst_pudp = (pud_t *)get_safe_page(GFP_ATOMIC);
>>> +		if (!dst_pudp)
>>> +			return -ENOMEM;
>>> +
>>> +		p4d_populate(NULL, dst_p4dp, dst_pudp);
>>> +	}
>>> +
>>> +	dst_pudp = pud_offset(dst_p4dp, start);
>>> +	src_pudp = pud_offset(src_p4dp, start);
>>> +
>>> +	do {
>>> +		pud_t pud = READ_ONCE(*src_pudp);
>>> +
>>> +		next = pud_addr_end(addr, end);
>>> +
>>> +		if (pud_none(pud))
>>> +			continue;
>>> +
>>> +		if (pud_leaf(pud)) {
>>> +			set_pud(dst_pudp, __pud(pud_val(pud) | pgprot_val(prot)));
>>> +		} else {
>>> +			ret = temp_pgtable_map_pmd(dst_pudp, src_pudp, addr, next, prot);
>>> +			if (ret)
>>> +				return -ENOMEM;
>>> +		}
>>> +	} while (dst_pudp++, src_pudp++, addr = next, addr != end);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static unsigned long temp_pgtable_map_p4d(pgd_t *dst_pgdp, pgd_t *src_pgdp,
>>> +					  unsigned long start, unsigned long end,
>>> +					  pgprot_t prot)
>>> +{
>>> +	unsigned long addr = start;
>>
>> Nit: you don't need the addr variable, you can rename start into addr
>> and directly work with it.
> sure.
>>
>>> +	unsigned long next;
>>> +	unsigned long ret;
>>> +	p4d_t *dst_p4dp;
>>> +	p4d_t *src_p4dp;
>>> +
>>> +	if (pgd_none(READ_ONCE(*dst_pgdp))) {
>>> +		dst_p4dp = (p4d_t *)get_safe_page(GFP_ATOMIC);
>>> +		if (!dst_p4dp)
>>> +			return -ENOMEM;
>>> +
>>> +		pgd_populate(NULL, dst_pgdp, dst_p4dp);
>>> +	}
>>> +
>>> +	dst_p4dp = p4d_offset(dst_pgdp, start);
>>> +	src_p4dp = p4d_offset(src_pgdp, start);
>>> +
>>> +	do {
>>> +		p4d_t p4d = READ_ONCE(*src_p4dp);
>>> +
>>> +		next = p4d_addr_end(addr, end);
>>> +
>>> +		if (p4d_none(READ_ONCE(*src_p4dp)))
>>
>> You should use p4d here: p4d_none(p4d)
> sure
>>
>>> +			continue;
>>> +
>>> +		if (p4d_leaf(p4d)) {
>>> +			set_p4d(dst_p4dp, __p4d(p4d_val(p4d) | pgprot_val(prot)));
>>
>> The "| pgprot_val(prot)" happens to work because PAGE_KERNEL will add
>> the PAGE_WRITE bit: I'd rather make it more clear by explicitly add
>> PAGE_WRITE.
> sure, this can be done.
>>
>>> +		} else {
>>> +			ret = temp_pgtable_map_pud(dst_p4dp, src_p4dp, addr, next, prot);
>>> +			if (ret)
>>> +				return -ENOMEM;
>>> +		}
>>> +	} while (dst_p4dp++, src_p4dp++, addr = next, addr != end);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static unsigned long temp_pgtable_mapping(pgd_t *pgdp)
>>> +{
>>> +	unsigned long end = (unsigned long)pfn_to_virt(max_low_pfn);
>>> +	unsigned long addr = PAGE_OFFSET;
>>> +	pgd_t *dst_pgdp = pgd_offset_pgd(pgdp, addr);
>>> +	pgd_t *src_pgdp = pgd_offset_k(addr);
>>> +	unsigned long next;
>>> +
>>> +	do {
>>> +		next = pgd_addr_end(addr, end);
>>> +		if (pgd_none(READ_ONCE(*src_pgdp)))
>>> +			continue;
>>> +
>>
>> We added the pgd_leaf test in kernel_page_present, let's add it here too.
> sure.
>>
>>> +		if (temp_pgtable_map_p4d(dst_pgdp, src_pgdp, addr, next, PAGE_KERNEL))
>>> +			return -ENOMEM;
>>> +	} while (dst_pgdp++, src_pgdp++, addr = next, addr != end);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static unsigned long temp_pgtable_text_mapping(pgd_t *pgdp, unsigned long addr)
>>> +{
>>> +	pgd_t *dst_pgdp = pgd_offset_pgd(pgdp, addr);
>>> +	pgd_t *src_pgdp = pgd_offset_k(addr);
>>> +
>>> +	if (pgd_none(READ_ONCE(*src_pgdp)))
>>> +		return -EFAULT;
>>> +
>>> +	if (temp_pgtable_map_p4d(dst_pgdp, src_pgdp, addr, addr, PAGE_KERNEL_EXEC))
>>> +		return -ENOMEM;
>>> +
>>> +	return 0;
>>> +}
>>
>> Ok so if we fall into a huge mapping, you add the exec permission to the
>> whole range, which could easily be 1GB. I think that either we can avoid
>> this step by mapping the whole linear mapping as executable, or we
>> actually use another pgd entry for this page that is not in the linear
>> mapping. The latter seems cleaner, what do you think?
> we can map the whole linear address to writable & executable, by doing this, we can avoid the remapping at the linear map again.
> we still need to use the same pgd entry for the non-linear mapping just like how it did at the swapper_pg_dir (linear and non-linear addr are within the range supported by the pgd).


Not sure I understand your last sentence


>>
>>> +
>>> +static unsigned long relocate_restore_code(void)
>>> +{
>>> +	unsigned long ret;
>>> +	void *page = (void *)get_safe_page(GFP_ATOMIC);
>>> +
>>> +	if (!page)
>>> +		return -ENOMEM;
>>> +
>>> +	copy_page(page, hibernate_core_restore_code);
>>> +
>>> +	/* Make the page containing the relocated code executable. */
>>> +	set_memory_x((unsigned long)page, 1);
>>> +
>>> +	ret = temp_pgtable_text_mapping(resume_pg_dir, (unsigned long)page);
>>> +	if (ret)
>>> +		return ret;
>>> +
>>> +	return (unsigned long)page;
>>> +}
>>> +
>>> +int swsusp_arch_resume(void)
>>> +{
>>> +	unsigned long ret;
>>> +
>>> +	/*
>>> +	 * Memory allocated by get_safe_page() will be dealt with by the hibernation core,
>>> +	 * we don't need to free it here.
>>> +	 */
>>> +	resume_pg_dir = (pgd_t *)get_safe_page(GFP_ATOMIC);
>>> +	if (!resume_pg_dir)
>>> +		return -ENOMEM;
>>> +
>>> +	/*
>>> +	 * The pages need to be writable when restoring the image.
>>> +	 * Create a second copy of page table just for the linear map.
>>> +	 * Use this temporary page table to restore the image.
>>> +	 */
>>> +	ret = temp_pgtable_mapping(resume_pg_dir);
>>> +	if (ret)
>>> +		return (int)ret;
>>
>> The temp_pgtable* functions should return an int to avoid this cast.


Did you note this comment too?


>>
>>
>>> +
>>> +	/* Move the restore code to a new page so that it doesn't get overwritten by itself. */
>>> +	relocated_restore_code = relocate_restore_code();
>>> +	if (relocated_restore_code == -ENOMEM)
>>> +		return -ENOMEM;
>>> +
>>> +	/*
>>> +	 * Map the __hibernate_cpu_resume() address to the temporary page table so that the
>>> +	 * restore code can jumps to it after finished restore the image. The next execution
>>> +	 * code doesn't find itself in a different address space after switching over to the
>>> +	 * original page table used by the hibernated image.
>>> +	 */
>>> +	ret = temp_pgtable_text_mapping(resume_pg_dir, (unsigned long)resume_hdr.restore_cpu_addr);
>>> +	if (ret)
>>> +		return ret;
>>> +
>>> +	hibernate_restore_image(resume_hdr.saved_satp, (PFN_DOWN(__pa(resume_pg_dir)) | satp_mode),
>>> +				resume_hdr.restore_cpu_addr);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +#ifdef CONFIG_PM_SLEEP_SMP
>>> +int hibernate_resume_nonboot_cpu_disable(void)
>>> +{
>>> +	if (sleep_cpu < 0) {
>>> +		pr_err("Failing to resume from hibernate on an unknown CPU\n");
>>> +		return -ENODEV;
>>> +	}
>>> +
>>> +	return freeze_secondary_cpus(sleep_cpu);
>>> +}
>>> +#endif
>>> +
>>> +static int __init riscv_hibernate_init(void)
>>> +{
>>> +	hibernate_cpu_context = kzalloc(sizeof(*hibernate_cpu_context), GFP_KERNEL);
>>> +
>>> +	if (WARN_ON(!hibernate_cpu_context))
>>> +		return -ENOMEM;
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +early_initcall(riscv_hibernate_init);
>>
>> Overall, it is now nicer with the the proper page table walk: but we can
>> now see that the code is exactly the same as arm64, what prevents us
>> from merging both somewhere in mm/?
> 1. low level page table bit definition not the same
> 2. Need to refactor code for both riscv and arm64
> 3. Need to verify the solution for both riscv and arm64 platforms (need someone who expertise on arm64)
> 4. Might need to extend the function to support other arch
> 5. Overall, it is do-able but the effort to support the above matters are huge.


Too bad, I really see benefits of avoiding code duplication, but that's 
up to you.

Thanks,

Alex


>