| Message ID | 20231207150348.82096-3-alexghiti@rivosinc.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Remove preventive sfence.vma | expand |
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@rivosinc.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)
On Thu, Dec 7, 2023 at 4:55 PM Christophe Leroy <christophe.leroy@csgroup.eu> wrote: > > > > 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@rivosinc.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) I left this patch so that people can easily test this without knowing what their uarch is actually doing, but it will very likely be dropped as a new extension has just been proposed for that. Thanks anyway, I should have been more clear in the patch title, Alex
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 + 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) + 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) + 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); + + 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)
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@rivosinc.com> --- arch/riscv/mm/init.c | 124 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 124 insertions(+)