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Subject: Re: [PATCH] riscv: Improve kasan population by using hugepages when
 possible
From:   Alex Ghiti <alex@ghiti.fr>
To:     Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>, kasan-dev@googlegroups.com,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
References: <20210201080024.844-1-alex@ghiti.fr>
 <74fef5c9-0632-3e12-e11b-81dd115a4be5@ghiti.fr>
Message-ID: <249567fd-d436-7e06-081c-65b1f9930b07@ghiti.fr>
Date:   Mon, 8 Feb 2021 14:46:34 -0500
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Le 2/2/21 ? 3:50 AM, Alex Ghiti a ?crit?:
> Hi,
> 
> Le 2/1/21 ? 3:00 AM, Alexandre Ghiti a ?crit?:
>> 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@ghiti.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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