From e921050022f1f12d5029d1487a7dfc46cde15523 Mon Sep 17 00:00:00 2001 From: Sergey Matyukevich Date: Sun, 26 Feb 2023 18:01:36 +0300 Subject: [PATCH 1/2] Revert "riscv: mm: notify remote harts about mmu cache updates" This reverts the remaining bits of commit 4bd1d80efb5a ("riscv: mm: notify remote harts harts about mmu cache updates"). According to bug reports, suggested approach to fix stale TLB entries is not sufficient. It needs to be replaced by a more robust solution. Fixes: 4bd1d80efb5a ("riscv: mm: notify remote harts about mmu cache updates") Reported-by: Zong Li Reported-by: Lad Prabhakar Signed-off-by: Sergey Matyukevich Cc: stable@vger.kernel.org Reviewed-by: Guo Ren Link: https://lore.kernel.org/r/20230226150137.1919750-2-geomatsi@gmail.com Signed-off-by: Palmer Dabbelt --- arch/riscv/include/asm/mmu.h | 2 -- arch/riscv/include/asm/tlbflush.h | 18 ------------------ arch/riscv/mm/context.c | 10 ---------- arch/riscv/mm/tlbflush.c | 28 +++++++++++++++++----------- 4 files changed, 17 insertions(+), 41 deletions(-) diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h index 5ff1f19fd45c..0099dc116168 100644 --- a/arch/riscv/include/asm/mmu.h +++ b/arch/riscv/include/asm/mmu.h @@ -19,8 +19,6 @@ typedef struct { #ifdef CONFIG_SMP /* A local icache flush is needed before user execution can resume. */ cpumask_t icache_stale_mask; - /* A local tlb flush is needed before user execution can resume. */ - cpumask_t tlb_stale_mask; #endif } mm_context_t; diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h index 907b9efd39a8..801019381dea 100644 --- a/arch/riscv/include/asm/tlbflush.h +++ b/arch/riscv/include/asm/tlbflush.h @@ -22,24 +22,6 @@ static inline void local_flush_tlb_page(unsigned long addr) { ALT_FLUSH_TLB_PAGE(__asm__ __volatile__ ("sfence.vma %0" : : "r" (addr) : "memory")); } - -static inline void local_flush_tlb_all_asid(unsigned long asid) -{ - __asm__ __volatile__ ("sfence.vma x0, %0" - : - : "r" (asid) - : "memory"); -} - -static inline void local_flush_tlb_page_asid(unsigned long addr, - unsigned long asid) -{ - __asm__ __volatile__ ("sfence.vma %0, %1" - : - : "r" (addr), "r" (asid) - : "memory"); -} - #else /* CONFIG_MMU */ #define local_flush_tlb_all() do { } while (0) #define local_flush_tlb_page(addr) do { } while (0) diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c index 80ce9caba8d2..7acbfbd14557 100644 --- a/arch/riscv/mm/context.c +++ b/arch/riscv/mm/context.c @@ -196,16 +196,6 @@ switch_mm_fast: if (need_flush_tlb) local_flush_tlb_all(); -#ifdef CONFIG_SMP - else { - cpumask_t *mask = &mm->context.tlb_stale_mask; - - if (cpumask_test_cpu(cpu, mask)) { - cpumask_clear_cpu(cpu, mask); - local_flush_tlb_all_asid(cntx & asid_mask); - } - } -#endif } static void set_mm_noasid(struct mm_struct *mm) diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c index ce7dfc81bb3f..37ed760d007c 100644 --- a/arch/riscv/mm/tlbflush.c +++ b/arch/riscv/mm/tlbflush.c @@ -5,7 +5,23 @@ #include #include #include -#include + +static inline void local_flush_tlb_all_asid(unsigned long asid) +{ + __asm__ __volatile__ ("sfence.vma x0, %0" + : + : "r" (asid) + : "memory"); +} + +static inline void local_flush_tlb_page_asid(unsigned long addr, + unsigned long asid) +{ + __asm__ __volatile__ ("sfence.vma %0, %1" + : + : "r" (addr), "r" (asid) + : "memory"); +} void flush_tlb_all(void) { @@ -15,7 +31,6 @@ void flush_tlb_all(void) static void __sbi_tlb_flush_range(struct mm_struct *mm, unsigned long start, unsigned long size, unsigned long stride) { - struct cpumask *pmask = &mm->context.tlb_stale_mask; struct cpumask *cmask = mm_cpumask(mm); unsigned int cpuid; bool broadcast; @@ -29,15 +44,6 @@ static void __sbi_tlb_flush_range(struct mm_struct *mm, unsigned long start, if (static_branch_unlikely(&use_asid_allocator)) { unsigned long asid = atomic_long_read(&mm->context.id); - /* - * TLB will be immediately flushed on harts concurrently - * executing this MM context. TLB flush on other harts - * is deferred until this MM context migrates there. - */ - cpumask_setall(pmask); - cpumask_clear_cpu(cpuid, pmask); - cpumask_andnot(pmask, pmask, cmask); - if (broadcast) { sbi_remote_sfence_vma_asid(cmask, start, size, asid); } else if (size <= stride) { From 82dd33fde0268cc622d3d1ac64971f3f61634142 Mon Sep 17 00:00:00 2001 From: Guo Ren Date: Sun, 26 Feb 2023 18:01:37 +0300 Subject: [PATCH 2/2] riscv: asid: Fixup stale TLB entry cause application crash After use_asid_allocator is enabled, the userspace application will crash by stale TLB entries. Because only using cpumask_clear_cpu without local_flush_tlb_all couldn't guarantee CPU's TLB entries were fresh. Then set_mm_asid would cause the user space application to get a stale value by stale TLB entry, but set_mm_noasid is okay. Here is the symptom of the bug: unhandled signal 11 code 0x1 (coredump) 0x0000003fd6d22524 <+4>: auipc s0,0x70 0x0000003fd6d22528 <+8>: ld s0,-148(s0) # 0x3fd6d92490 => 0x0000003fd6d2252c <+12>: ld a5,0(s0) (gdb) i r s0 s0 0x8082ed1cc3198b21 0x8082ed1cc3198b21 (gdb) x /2x 0x3fd6d92490 0x3fd6d92490: 0xd80ac8a8 0x0000003f The core dump file shows that register s0 is wrong, but the value in memory is correct. Because 'ld s0, -148(s0)' used a stale mapping entry in TLB and got a wrong result from an incorrect physical address. When the task ran on CPU0, which loaded/speculative-loaded the value of address(0x3fd6d92490), then the first version of the mapping entry was PTWed into CPU0's TLB. When the task switched from CPU0 to CPU1 (No local_tlb_flush_all here by asid), it happened to write a value on the address (0x3fd6d92490). It caused do_page_fault -> wp_page_copy -> ptep_clear_flush -> ptep_get_and_clear & flush_tlb_page. The flush_tlb_page used mm_cpumask(mm) to determine which CPUs need TLB flush, but CPU0 had cleared the CPU0's mm_cpumask in the previous switch_mm. So we only flushed the CPU1 TLB and set the second version mapping of the PTE. When the task switched from CPU1 to CPU0 again, CPU0 still used a stale TLB mapping entry which contained a wrong target physical address. It raised a bug when the task happened to read that value. CPU0 CPU1 - switch 'task' in - read addr (Fill stale mapping entry into TLB) - switch 'task' out (no tlb_flush) - switch 'task' in (no tlb_flush) - write addr cause pagefault do_page_fault() (change to new addr mapping) wp_page_copy() ptep_clear_flush() ptep_get_and_clear() & flush_tlb_page() write new value into addr - switch 'task' out (no tlb_flush) - switch 'task' in (no tlb_flush) - read addr again (Use stale mapping entry in TLB) get wrong value from old phyical addr, BUG! The solution is to keep all CPUs' footmarks of cpumask(mm) in switch_mm, which could guarantee to invalidate all stale TLB entries during TLB flush. Fixes: 65d4b9c53017 ("RISC-V: Implement ASID allocator") Signed-off-by: Guo Ren Signed-off-by: Guo Ren Tested-by: Lad Prabhakar Tested-by: Zong Li Tested-by: Sergey Matyukevich Cc: Anup Patel Cc: Palmer Dabbelt Cc: stable@vger.kernel.org Reviewed-by: Andrew Jones Link: https://lore.kernel.org/r/20230226150137.1919750-3-geomatsi@gmail.com Signed-off-by: Palmer Dabbelt --- arch/riscv/mm/context.c | 30 ++++++++++++++++++++---------- 1 file changed, 20 insertions(+), 10 deletions(-) diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c index 7acbfbd14557..0f784e3d307b 100644 --- a/arch/riscv/mm/context.c +++ b/arch/riscv/mm/context.c @@ -205,12 +205,24 @@ static void set_mm_noasid(struct mm_struct *mm) local_flush_tlb_all(); } -static inline void set_mm(struct mm_struct *mm, unsigned int cpu) +static inline void set_mm(struct mm_struct *prev, + struct mm_struct *next, unsigned int cpu) { - if (static_branch_unlikely(&use_asid_allocator)) - set_mm_asid(mm, cpu); - else - set_mm_noasid(mm); + /* + * The mm_cpumask indicates which harts' TLBs contain the virtual + * address mapping of the mm. Compared to noasid, using asid + * can't guarantee that stale TLB entries are invalidated because + * the asid mechanism wouldn't flush TLB for every switch_mm for + * performance. So when using asid, keep all CPUs footmarks in + * cpumask() until mm reset. + */ + cpumask_set_cpu(cpu, mm_cpumask(next)); + if (static_branch_unlikely(&use_asid_allocator)) { + set_mm_asid(next, cpu); + } else { + cpumask_clear_cpu(cpu, mm_cpumask(prev)); + set_mm_noasid(next); + } } static int __init asids_init(void) @@ -264,7 +276,8 @@ static int __init asids_init(void) } early_initcall(asids_init); #else -static inline void set_mm(struct mm_struct *mm, unsigned int cpu) +static inline void set_mm(struct mm_struct *prev, + struct mm_struct *next, unsigned int cpu) { /* Nothing to do here when there is no MMU */ } @@ -317,10 +330,7 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next, */ cpu = smp_processor_id(); - cpumask_clear_cpu(cpu, mm_cpumask(prev)); - cpumask_set_cpu(cpu, mm_cpumask(next)); - - set_mm(next, cpu); + set_mm(prev, next, cpu); flush_icache_deferred(next, cpu); }