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Message-ID: <249567fd-d436-7e06-081c-65b1f9930b07@ghiti.fr>
Date: Mon, 8 Feb 2021 14:46:34 -0500
From: Alex Ghiti <alex@...ti.fr>
To: Andrey Ryabinin <aryabinin@...tuozzo.com>,
Alexander Potapenko <glider@...gle.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>, kasan-dev@...glegroups.com,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: Improve kasan population by using hugepages when
possible
Le 2/2/21 à 3:50 AM, Alex Ghiti a écrit :
> Hi,
>
> Le 2/1/21 à 3:00 AM, Alexandre Ghiti a écrit :
>> Kasan function that populates the shadow regions used to allocate them
>> page by page and did not take advantage of hugepages, so fix this by
>> trying to allocate hugepages of 1GB and fallback to 2MB hugepages or 4K
>> pages in case it fails.
>>
>> This reduces the page table memory consumption and improves TLB usage,
>> as shown below:
>>
>> Before this patch:
>>
>> ---[ Kasan shadow start ]---
>> 0xffffffc000000000-0xffffffc400000000 0x00000000818ef000 16G
>> PTE . A . . . . R V
>> 0xffffffc400000000-0xffffffc447fc0000 0x00000002b7f4f000 1179392K
>> PTE D A . . . W R V
>> 0xffffffc480000000-0xffffffc800000000 0x00000000818ef000 14G
>> PTE . A . . . . R V
>> ---[ Kasan shadow end ]---
>>
>> After this patch:
>>
>> ---[ Kasan shadow start ]---
>> 0xffffffc000000000-0xffffffc400000000 0x00000000818ef000 16G
>> PTE . A . . . . R V
>> 0xffffffc400000000-0xffffffc440000000 0x0000000240000000 1G
>> PGD D A . . . W R V
>> 0xffffffc440000000-0xffffffc447e00000 0x00000002b7e00000 126M
>> PMD D A . . . W R V
>> 0xffffffc447e00000-0xffffffc447fc0000 0x00000002b818f000 1792K
>> PTE D A . . . W R V
>> 0xffffffc480000000-0xffffffc800000000 0x00000000818ef000 14G
>> PTE . A . . . . R V
>> ---[ Kasan shadow end ]---
>>
>> Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
>> ---
>> arch/riscv/mm/kasan_init.c | 101 +++++++++++++++++++++++++++----------
>> 1 file changed, 73 insertions(+), 28 deletions(-)
>>
>> diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c
>> index a8a2ffd9114a..8f11b73018b1 100644
>> --- a/arch/riscv/mm/kasan_init.c
>> +++ b/arch/riscv/mm/kasan_init.c
>> @@ -47,37 +47,82 @@ asmlinkage void __init kasan_early_init(void)
>> local_flush_tlb_all();
>> }
>> -static void __init populate(void *start, void *end)
>> +static void kasan_populate_pte(pmd_t *pmd, unsigned long vaddr,
>> unsigned long end)
>> +{
>> + phys_addr_t phys_addr;
>> + pte_t *ptep = memblock_alloc(PTRS_PER_PTE * sizeof(pte_t),
>> PAGE_SIZE);
>> +
>> + do {
>> + phys_addr = memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
>> + set_pte(ptep, pfn_pte(PFN_DOWN(phys_addr), PAGE_KERNEL));
>> + } while (ptep++, vaddr += PAGE_SIZE, vaddr != end);
>> +
>> + set_pmd(pmd, pfn_pmd(PFN_DOWN(__pa(ptep)), PAGE_TABLE));
>> +}
>> +
>> +static void kasan_populate_pmd(pgd_t *pgd, unsigned long vaddr,
>> unsigned long end)
>> +{
>> + phys_addr_t phys_addr;
>> + pmd_t *pmdp = memblock_alloc(PTRS_PER_PMD * sizeof(pmd_t),
>> PAGE_SIZE);
>> + unsigned long next;
>> +
>> + do {
>> + next = pmd_addr_end(vaddr, end);
>> +
>> + if (IS_ALIGNED(vaddr, PMD_SIZE) && (next - vaddr) >= PMD_SIZE) {
>> + phys_addr = memblock_phys_alloc(PMD_SIZE, PMD_SIZE);
>> + if (phys_addr) {
>> + set_pmd(pmdp, pfn_pmd(PFN_DOWN(phys_addr),
>> PAGE_KERNEL));
>> + continue;
>> + }
>> + }
>> +
>> + kasan_populate_pte(pmdp, vaddr, end);
>> + } while (pmdp++, vaddr = next, vaddr != end);
>> +
>> + /*
>> + * Wait for the whole PGD to be populated before setting the PGD in
>> + * the page table, otherwise, if we did set the PGD before
>> populating
>> + * it entirely, memblock could allocate a page at a physical address
>> + * where KASAN is not populated yet and then we'd get a page fault.
>> + */
>> + set_pgd(pgd, pfn_pgd(PFN_DOWN(__pa(pmdp)), PAGE_TABLE));
>
> In case the PMD was filled entirely, PFN_DOWN(__pa(pmdp)) will point to
> the next physical page, which is wrong. The same problem happens on the
> other levels too.
>
> I'll fix that in a v2 later today.
>
> Alex
>
>> +}
>> +
>> +static void kasan_populate_pgd(unsigned long vaddr, unsigned long end)
>> +{
>> + phys_addr_t phys_addr;
>> + pgd_t *pgdp = pgd_offset_k(vaddr);
>> + unsigned long next;
>> +
>> + do {
>> + next = pgd_addr_end(vaddr, end);
>> +
>> + if (IS_ALIGNED(vaddr, PGDIR_SIZE) && (next - vaddr) >=
>> PGDIR_SIZE) {
>> + phys_addr = memblock_phys_alloc(PGDIR_SIZE, PGDIR_SIZE);
>> + if (phys_addr) {
>> + set_pgd(pgdp, pfn_pgd(PFN_DOWN(phys_addr),
>> PAGE_KERNEL));
>> + continue;
>> + }
>> + }
>> +
>> + kasan_populate_pmd(pgdp, vaddr, end);
>> + } while (pgdp++, vaddr = next, vaddr != end);
>> +}
>> +
>> +/*
>> + * This function populates KASAN shadow region focusing on hugepages in
>> + * order to minimize the page table cost and TLB usage too.
>> + * Note that start must be PGDIR_SIZE-aligned in SV39 which amounts
>> to be
>> + * 1G aligned (that represents a 8G alignment constraint on virtual
>> address
>> + * ranges because of KASAN_SHADOW_SCALE_SHIFT).
>> + */
>> +static void __init kasan_populate(void *start, void *end)
>> {
>> - unsigned long i, offset;
>> unsigned long vaddr = (unsigned long)start & PAGE_MASK;
>> unsigned long vend = PAGE_ALIGN((unsigned long)end);
>> - unsigned long n_pages = (vend - vaddr) / PAGE_SIZE;
>> - unsigned long n_ptes =
>> - ((n_pages + PTRS_PER_PTE) & -PTRS_PER_PTE) / PTRS_PER_PTE;
>> - unsigned long n_pmds =
>> - ((n_ptes + PTRS_PER_PMD) & -PTRS_PER_PMD) / PTRS_PER_PMD;
>> -
>> - pte_t *pte =
>> - memblock_alloc(n_ptes * PTRS_PER_PTE * sizeof(pte_t),
>> PAGE_SIZE);
>> - pmd_t *pmd =
>> - memblock_alloc(n_pmds * PTRS_PER_PMD * sizeof(pmd_t),
>> PAGE_SIZE);
>> - pgd_t *pgd = pgd_offset_k(vaddr);
>> -
>> - for (i = 0; i < n_pages; i++) {
>> - phys_addr_t phys = memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
>> - set_pte(&pte[i], pfn_pte(PHYS_PFN(phys), PAGE_KERNEL));
>> - }
>> -
>> - for (i = 0, offset = 0; i < n_ptes; i++, offset += PTRS_PER_PTE)
>> - set_pmd(&pmd[i],
>> - pfn_pmd(PFN_DOWN(__pa(&pte[offset])),
>> - __pgprot(_PAGE_TABLE)));
>> - for (i = 0, offset = 0; i < n_pmds; i++, offset += PTRS_PER_PMD)
>> - set_pgd(&pgd[i],
>> - pfn_pgd(PFN_DOWN(__pa(&pmd[offset])),
>> - __pgprot(_PAGE_TABLE)));
>> + kasan_populate_pgd(vaddr, vend);
>> local_flush_tlb_all();
>> memset(start, 0, end - start);
>> @@ -99,7 +144,7 @@ void __init kasan_init(void)
>> if (start >= end)
>> break;
>> - populate(kasan_mem_to_shadow(start), kasan_mem_to_shadow(end));
>> + kasan_populate(kasan_mem_to_shadow(start),
>> kasan_mem_to_shadow(end));
>> };
>> for (i = 0; i < PTRS_PER_PTE; i++)
>>
Palmer, you can drop this one as I split it and fixed it in my "Kasan
improvements and fixes" series.
Thanks,
Alex
>
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