[RFC PATCH 4/4] arm64: support flipped VA and 52-bit kernel VA
piliu
piliu at redhat.com
Thu Jan 14 20:41:17 EST 2021
On 1/15/21 8:40 AM, HAGIO KAZUHITO(萩尾 一仁) wrote:
> Hi Pingfan, Bhupesh,
>
> Thank you for your comments!
>
> -----Original Message-----
>> Hi Kazu,
>>
>> On Thu, Jan 14, 2021 at 3:33 PM piliu <piliu at redhat.com> wrote:
>>>
>>>
>>>
>>> On 1/14/21 4:25 PM, kazuhito.hagio at gmail.com wrote:
>>>> From: Kazuhito Hagio <k-hagio-ab at nec.com>
>>>>
>>>> Based on Bhupesh's patch and contains Pingfan's idea.
>>>>
>>>> Signed-off-by: Bhupesh Sharma <bhsharma at redhat.com>
>>>> Signed-off-by: Kazuhito Hagio <k-hagio-ab at nec.com>
>>>> ---
>>>> arch/arm64.c | 95 ++++++++++++++++++++++++++++++++++++++++++++++++----------
>>>> makedumpfile.c | 2 ++
>>>> makedumpfile.h | 1 +
>>>> 3 files changed, 83 insertions(+), 15 deletions(-)
>>>>
>>>> diff --git a/arch/arm64.c b/arch/arm64.c
>>>> index 61ec89a..4ece19d 100644
>>>> --- a/arch/arm64.c
>>>> +++ b/arch/arm64.c
>>>> @@ -47,6 +47,8 @@ typedef struct {
>>>> static int lpa_52_bit_support_available;
>>>> static int pgtable_level;
>>>> static int va_bits;
>>>> +static int vabits_actual;
>>>> +static int flipped_va;
>>>> static unsigned long kimage_voffset;
>>>>
>>>> #define SZ_4K 4096
>>>> @@ -58,7 +60,6 @@ static unsigned long kimage_voffset;
>>>> #define PAGE_OFFSET_42 ((0xffffffffffffffffUL) << 42)
>>>> #define PAGE_OFFSET_47 ((0xffffffffffffffffUL) << 47)
>>>> #define PAGE_OFFSET_48 ((0xffffffffffffffffUL) << 48)
>>>> -#define PAGE_OFFSET_52 ((0xffffffffffffffffUL) << 52)
>>>>
>>>> #define pgd_val(x) ((x).pgd)
>>>> #define pud_val(x) (pgd_val((x).pgd))
>>>> @@ -218,12 +219,20 @@ pmd_page_paddr(pmd_t pmd)
>>>> #define pte_index(vaddr) (((vaddr) >> PAGESHIFT()) & (PTRS_PER_PTE - 1))
>>>> #define pte_offset(dir, vaddr) (pmd_page_paddr((*dir)) + pte_index(vaddr) *
>> sizeof(pte_t))
>>>>
>>>> +/*
>>>> + * The linear kernel range starts at the bottom of the virtual address
>>>> + * space. Testing the top bit for the start of the region is a
>>>> + * sufficient check and avoids having to worry about the tag.
>>>> + */
>>>> +#define is_linear_addr(addr) (flipped_va ? \
>>>> + (!((unsigned long)(addr) & (1UL << (vabits_actual - 1)))) : \
>>>> + (!!((unsigned long)(addr) & (1UL << (vabits_actual - 1)))))
>>>> +
>>>> static unsigned long long
>>>> __pa(unsigned long vaddr)
>>>> {
>>>> - if (kimage_voffset == NOT_FOUND_NUMBER ||
>>>> - (vaddr >= PAGE_OFFSET))
>>>> - return (vaddr - PAGE_OFFSET + info->phys_base);
>>>> + if (kimage_voffset == NOT_FOUND_NUMBER || is_linear_addr(vaddr))
>>>> + return ((vaddr & ~PAGE_OFFSET) + info->phys_base);
>>>> else
>>>> return (vaddr - kimage_voffset);
>>>> }
>>>> @@ -253,6 +262,7 @@ static int calculate_plat_config(void)
>>>> (PAGESIZE() == SZ_64K && va_bits == 42)) {
>>>> pgtable_level = 2;
>>>> } else if ((PAGESIZE() == SZ_64K && va_bits == 48) ||
>>>> + (PAGESIZE() == SZ_64K && va_bits == 52) ||
>>>> (PAGESIZE() == SZ_4K && va_bits == 39) ||
>>>> (PAGESIZE() == SZ_16K && va_bits == 47)) {
>>>> pgtable_level = 3;
>>>> @@ -263,6 +273,7 @@ static int calculate_plat_config(void)
>>>> PAGESIZE(), va_bits);
>>>> return FALSE;
>>>> }
>>>> + DEBUG_MSG("pgtable_level: %d\n", pgtable_level);
>>>>
>>>> return TRUE;
>>>> }
>>>> @@ -383,22 +394,54 @@ get_va_bits_from_stext_arm64(void)
>>>> return TRUE;
>>>> }
>>>>
>>>> +static void
>>>> +get_page_offset_arm64(void)
>>>> +{
>>>> + ulong page_end;
>>>> + int vabits_min;
>>>> +
>>>> + /*
>>>> + * See arch/arm64/include/asm/memory.h for more details of
>>>> + * the PAGE_OFFSET calculation.
>>>> + */
>>>> + vabits_min = (va_bits > 48) ? 48 : va_bits;
>>>> + page_end = -(1UL << (vabits_min - 1));
>>>> +
>>>> + if (SYMBOL(_stext) > page_end) {
>>>> + flipped_va = TRUE;
>>>> + info->page_offset = -(1UL << vabits_actual);
>>>> + } else {
>>>> + flipped_va = FALSE;
>>>> + info->page_offset = -(1UL << (vabits_actual - 1));
>>>> + }
>>>> +
>>>> + DEBUG_MSG("page_offset : %lx (from page_end check)\n",
>>>> + info->page_offset);
>>>> +}
>>>> +
>>>> int
>>>> get_machdep_info_arm64(void)
>>>> {
>>>> + /* Check if va_bits is still not initialized. If still 0, call
>>>> + * get_versiondep_info() to initialize the same.
>>>> + */
>>>> + if (!va_bits)
>>>> + get_versiondep_info_arm64();
>>>> +
>>>> /* Determine if the PA address range is 52-bits: ARMv8.2-LPA */
>>>> if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER) {
>>>> info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
>>>> + DEBUG_MSG("max_physmem_bits : %ld (vmcoreinfo)\n", info->max_physmem_bits);
>>>> if (info->max_physmem_bits == 52)
>>>> lpa_52_bit_support_available = 1;
>>>> - } else
>>>> - info->max_physmem_bits = 48;
>>>> + } else {
>>>> + if (va_bits == 52)
>>>> + info->max_physmem_bits = 52; /* just guess */
>>>> + else
>>>> + info->max_physmem_bits = 48;
>>>>
>>>> - /* Check if va_bits is still not initialized. If still 0, call
>>>> - * get_versiondep_info() to initialize the same.
>>>> - */
>>>> - if (!va_bits)
>>>> - get_versiondep_info_arm64();
>>>> + DEBUG_MSG("max_physmem_bits : %ld (guess)\n", info->max_physmem_bits);
>>>> + }
>>>>
>>>> if (!calculate_plat_config()) {
>>>> ERRMSG("Can't determine platform config values\n");
>>>> @@ -409,7 +452,6 @@ get_machdep_info_arm64(void)
>>>> info->section_size_bits = SECTIONS_SIZE_BITS;
>>>>
>>>> DEBUG_MSG("kimage_voffset : %lx\n", kimage_voffset);
>>>> - DEBUG_MSG("max_physmem_bits : %ld\n", info->max_physmem_bits);
>>>> DEBUG_MSG("section_size_bits: %ld\n", info->section_size_bits);
>>>>
>>>> return TRUE;
>>>> @@ -444,10 +486,33 @@ get_versiondep_info_arm64(void)
>>>> return FALSE;
>>>> }
>>>>
>>>> - info->page_offset = (0xffffffffffffffffUL) << (va_bits - 1);
>>>> + /*
>>>> + * See TCR_EL1, Translation Control Register (EL1) register
>>>> + * description in the ARMv8 Architecture Reference Manual.
>>>> + * Basically, we can use the TCR_EL1.T1SZ
>>>> + * value to determine the virtual addressing range supported
>>>> + * in the kernel-space (i.e. vabits_actual) since Linux 5.9.
>>>> + */
>>>> + if (NUMBER(TCR_EL1_T1SZ) != NOT_FOUND_NUMBER) {
>>>> + vabits_actual = 64 - NUMBER(TCR_EL1_T1SZ);
>>>> + DEBUG_MSG("vabits_actual : %d (vmcoreinfo)\n", vabits_actual);
>>>> + } else if ((va_bits == 52) && (SYMBOL(mem_section) != NOT_FOUND_SYMBOL)) {
>>>> + /*
>>>> + * Linux 5.4 through 5.10 have the following linear space:
>>>> + * 48-bit: 0xffff000000000000 - 0xffff7fffffffffff
>>>> + * 58-bit: 0xfff0000000000000 - 0xfff7ffffffffffff
>>>> + */
>>>> + if (SYMBOL(mem_section) & (1UL << (52 - 1)))
>>>
>>> Sorry but I do not think any SYMBOL(x) is inside the range of linear
>>> mapping address. All of them should be beyond kimage_vaddr.
>
> As for this, SYMBOL(mem_section) is a bit special and shows the value in the
> mem_section variable, not the address of it, by kernel commit a0b1280368d1.
>
> Actually on my tiny arm64 board..
>
> # strings /proc/kcore | less
> ...
> OSRELEASE=5.4.0-1025-raspi
> PAGESIZE=4096
> SYMBOL(init_uts_ns)=ffffd6db0fa10568
> SYMBOL(node_online_map)=ffffd6db0fa0a808
> SYMBOL(swapper_pg_dir)=ffffd6db0f42b000
> SYMBOL(_stext)=ffffd6db0e481000
> SYMBOL(vmap_area_list)=ffffd6db0fa51680
> SYMBOL(mem_map)=ffffd6db0fbc0240
> SYMBOL(contig_page_data)=ffffd6db0faed6c0
> SYMBOL(mem_section)=ffff0000eb809300 <<--
> LENGTH(mem_section)=1024
> SIZE(mem_section)=16
> OFFSET(mem_section.section_mem_map)=0
> ...
> NUMBER(VA_BITS)=48
>
> So at least if the kernel is configured with CONFIG_SPARSEMEM_EXTREME,
You are right. Exactly, your method works in this case.
> I thought this would work. This is just a user tool effort to broaden
> supported kernels, instead of necessary information from the kernel,
> no need to support all kernels.
I hold a private opinion against the solution based on kernel version,
since it raises extra effort to cope with different releases which back
port some upstream patches without advancing kernel version.
>
> And the current makedumpfile's implementation, SYMBOL(mem_section) is set
> to the address of the mem_section variable with -x option, so I wrote on
> the cover letter that this patchset doesn't support "with -x option if
> vabits_actual=52" case yet.
>
>>>
>>> Having vabits_actual is introduced and precise to resolve
>>> is_lm_address(), but if it is not available, could we survive?
>>>
>>> _PAGE_OFFSET(52) < _PAGE_END(52) < _PAGE_OFFSET(48) < _PAGE_END(48)
>>> Translating into numbers:
>>> 0xfff0000000000000 < 0xfff8000000000000 < 0xffff000000000000 <
>>> 0xffff800000000000
>>>
>>> Refer to linux/Documentation/arm64/memory.rst, the line
>>> ffffa00010000000 fffff81ffffeffff ~88TB vmalloc
>>>
>>> It comes to the conclusion that any symbol > SYMBOL(_text) > _PAGE_END(48).
>>>
>>> So is_lm_address() can looks like
>>> if (addr > _PAGE_END(48)), it is kimage
>>> else, it is linear mapping
>
> This sounds good and will work.
>
>>>
>>> So even more aggressive, we can exclude the need of vabits_actual
>>> totally in this patch.
>
> Interesting, but if vabits_actual is not available, I wonder how we can
> get info->page_offset. Seems it's used mainly for p2v conversion and
Ashamed. I will make the best of the fact that va_bits=52 kernel only
has _PAGE_OFFSET(52). It looks not elegant, but should work.
Regards,
Pingfan
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