[RFC PATCH 4/4] arm64: support flipped VA and 52-bit kernel VA
Bhupesh SHARMA
bhupesh.linux at gmail.com
Thu Jan 14 13:25:40 EST 2021
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.
>
> 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
>
> So even more aggressive, we can exclude the need of vabits_actual
> totally in this patch.
As Pingfan noted, this approach still has issues and it failed on my
arm64 board in the limited testing I did today.
I will do some more testing tomorrow and come back with an approach
which addresses the same and also takes into account Pingfan's
concerns.
Thanks,
Bhupesh
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