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Message-ID: <6e3fb7b0-f47d-4d2f-b1b8-3ecc047b9ebf@csgroup.eu>
Date: Thu, 7 Dec 2023 15:55:39 +0000
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Alexandre Ghiti <alexghiti@...osinc.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
Michael Ellerman <mpe@...erman.id.au>,
Nicholas Piggin <npiggin@...il.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Andrew Morton <akpm@...ux-foundation.org>,
Ved Shanbhogue <ved@...osinc.com>,
Matt Evans <mev@...osinc.com>,
Dylan Jhong <dylan@...estech.com>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
"linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH RFC/RFT 2/4] riscv: Add a runtime detection of invalid TLB
entries caching
Le 07/12/2023 à 16:03, Alexandre Ghiti a écrit :
> This mechanism allows to completely bypass the sfence.vma introduced by
> the previous commit for uarchs that do not cache invalid TLB entries.
>
> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
> ---
> arch/riscv/mm/init.c | 124 +++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 124 insertions(+)
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 379403de6c6f..2e854613740c 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -56,6 +56,8 @@ bool pgtable_l5_enabled = IS_ENABLED(CONFIG_64BIT) && !IS_ENABLED(CONFIG_XIP_KER
> EXPORT_SYMBOL(pgtable_l4_enabled);
> EXPORT_SYMBOL(pgtable_l5_enabled);
>
> +bool tlb_caching_invalid_entries;
> +
> phys_addr_t phys_ram_base __ro_after_init;
> EXPORT_SYMBOL(phys_ram_base);
>
> @@ -750,6 +752,18 @@ static void __init disable_pgtable_l4(void)
> satp_mode = SATP_MODE_39;
> }
>
> +static void __init enable_pgtable_l5(void)
> +{
> + pgtable_l5_enabled = true;
> + satp_mode = SATP_MODE_57;
> +}
> +
> +static void __init enable_pgtable_l4(void)
> +{
> + pgtable_l4_enabled = true;
> + satp_mode = SATP_MODE_48;
> +}
> +
> static int __init print_no4lvl(char *p)
> {
> pr_info("Disabled 4-level and 5-level paging");
> @@ -826,6 +840,112 @@ static __init void set_satp_mode(uintptr_t dtb_pa)
> memset(early_pud, 0, PAGE_SIZE);
> memset(early_pmd, 0, PAGE_SIZE);
> }
> +
> +/* Determine at runtime if the uarch caches invalid TLB entries */
> +static __init void set_tlb_caching_invalid_entries(void)
> +{
> +#define NR_RETRIES_CACHING_INVALID_ENTRIES 50
Looks odd to have macros nested in the middle of a function.
> + uintptr_t set_tlb_caching_invalid_entries_pmd = ((unsigned long)set_tlb_caching_invalid_entries) & PMD_MASK;
> + // TODO the test_addr as defined below could go into another pud...
> + uintptr_t test_addr = set_tlb_caching_invalid_entries_pmd + 2 * PMD_SIZE;
> + pmd_t valid_pmd;
> + u64 satp;
> + int i = 0;
> +
> + /* To ease the page table creation */
> + disable_pgtable_l5();
> + disable_pgtable_l4();
> +
> + /* Establish a mapping for set_tlb_caching_invalid_entries() in sv39 */
> + create_pgd_mapping(early_pg_dir,
> + set_tlb_caching_invalid_entries_pmd,
> + (uintptr_t)early_pmd,
> + PGDIR_SIZE, PAGE_TABLE);
> +
> + /* Handle the case where set_tlb_caching_invalid_entries straddles 2 PMDs */
> + create_pmd_mapping(early_pmd,
> + set_tlb_caching_invalid_entries_pmd,
> + set_tlb_caching_invalid_entries_pmd,
> + PMD_SIZE, PAGE_KERNEL_EXEC);
> + create_pmd_mapping(early_pmd,
> + set_tlb_caching_invalid_entries_pmd + PMD_SIZE,
> + set_tlb_caching_invalid_entries_pmd + PMD_SIZE,
> + PMD_SIZE, PAGE_KERNEL_EXEC);
> +
> + /* Establish an invalid mapping */
> + create_pmd_mapping(early_pmd, test_addr, 0, PMD_SIZE, __pgprot(0));
> +
> + /* Precompute the valid pmd here because the mapping for pfn_pmd() won't exist */
> + valid_pmd = pfn_pmd(PFN_DOWN(set_tlb_caching_invalid_entries_pmd), PAGE_KERNEL);
> +
> + local_flush_tlb_all();
> + satp = PFN_DOWN((uintptr_t)&early_pg_dir) | SATP_MODE_39;
> + csr_write(CSR_SATP, satp);
> +
> + /*
> + * Set stvec to after the trapping access, access this invalid mapping
> + * and legitimately trap
> + */
> + // TODO: Should I save the previous stvec?
> +#define ASM_STR(x) __ASM_STR(x)
Looks odd to have macros nested in the middle of a function.
> + asm volatile(
> + "la a0, 1f \n"
> + "csrw " ASM_STR(CSR_TVEC) ", a0 \n"
> + "ld a0, 0(%0) \n"
> + ".align 2 \n"
> + "1: \n"
> + :
> + : "r" (test_addr)
> + : "a0"
> + );
> +
> + /* Now establish a valid mapping to check if the invalid one is cached */
> + early_pmd[pmd_index(test_addr)] = valid_pmd;
> +
> + /*
> + * Access the valid mapping multiple times: indeed, we can't use
> + * sfence.vma as a barrier to make sure the cpu did not reorder accesses
> + * so we may trap even if the uarch does not cache invalid entries. By
> + * trying a few times, we make sure that those uarchs will see the right
> + * mapping at some point.
> + */
> +
> + i = NR_RETRIES_CACHING_INVALID_ENTRIES;
> +
> +#define ASM_STR(x) __ASM_STR(x)
Deplicate define ?
> + asm_volatile_goto(
> + "la a0, 1f \n"
> + "csrw " ASM_STR(CSR_TVEC) ", a0 \n"
> + ".align 2 \n"
> + "1: \n"
> + "addi %0, %0, -1 \n"
> + "blt %0, zero, %l[caching_invalid_entries] \n"
> + "ld a0, 0(%1) \n"
> + :
> + : "r" (i), "r" (test_addr)
> + : "a0"
> + : caching_invalid_entries
> + );
> +
> + csr_write(CSR_SATP, 0ULL);
> + local_flush_tlb_all();
> +
> + /* If we don't trap, the uarch does not cache invalid entries! */
> + tlb_caching_invalid_entries = false;
> + goto clean;
> +
> +caching_invalid_entries:
> + csr_write(CSR_SATP, 0ULL);
> + local_flush_tlb_all();
> +
> + tlb_caching_invalid_entries = true;
> +clean:
> + memset(early_pg_dir, 0, PAGE_SIZE);
> + memset(early_pmd, 0, PAGE_SIZE);
Use clear_page() instead ?
> +
> + enable_pgtable_l4();
> + enable_pgtable_l5();
> +}
> #endif
>
> /*
> @@ -1072,6 +1192,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> #endif
>
> #if defined(CONFIG_64BIT) && !defined(CONFIG_XIP_KERNEL)
> + set_tlb_caching_invalid_entries();
> set_satp_mode(dtb_pa);
> #endif
>
> @@ -1322,6 +1443,9 @@ static void __init setup_vm_final(void)
> local_flush_tlb_all();
>
> pt_ops_set_late();
> +
> + pr_info("uarch caches invalid entries: %s",
> + tlb_caching_invalid_entries ? "yes" : "no");
> }
> #else
> asmlinkage void __init setup_vm(uintptr_t dtb_pa)
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