Messages in this thread Patch in this message | | | Date | Wed, 03 Apr 2024 14:44:21 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCH] arm64: tlb: Fix TLBI RANGE operand |
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On Wed, 03 Apr 2024 12:37:30 +0100, Gavin Shan <gshan@redhat.com> wrote: > > On 4/3/24 18:58, Marc Zyngier wrote: > > On Wed, 03 Apr 2024 07:49:29 +0100, > > Gavin Shan <gshan@redhat.com> wrote: > >> > >> KVM/arm64 relies on TLBI RANGE feature to flush TLBs when the dirty > >> bitmap is collected by VMM and the corresponding PTEs need to be > >> write-protected again. Unfortunately, the operand passed to the TLBI > >> RANGE instruction isn't correctly sorted out by commit d1d3aa98b1d4 > >> ("arm64: tlb: Use the TLBI RANGE feature in arm64"). It leads to > >> crash on the destination VM after live migration because some of the > >> dirty pages are missed. > >> > >> For example, I have a VM where 8GB memory is assigned, starting from > >> 0x40000000 (1GB). Note that the host has 4KB as the base page size. > >> All TLBs for VM can be covered by one TLBI RANGE operation. However, > >> I receives 0xffff708000040000 as the operand, which is wrong and the > >> correct one should be 0x00007f8000040000. From the wrong operand, we > >> have 3 and 1 for SCALE (bits[45:44) and NUM (bits943:39], only 1GB > >> instead of 8GB memory is covered. > >> > >> Fix the macro __TLBI_RANGE_NUM() so that the correct NUM and TLBI > >> RANGE operand are provided. > >> > >> Fixes: d1d3aa98b1d4 ("arm64: tlb: Use the TLBI RANGE feature in arm64") > >> Cc: stable@kernel.org # v5.10+ > >> Reported-by: Yihuang Yu <yihyu@redhat.com> > >> Signed-off-by: Gavin Shan <gshan@redhat.com> > >> --- > >> arch/arm64/include/asm/tlbflush.h | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h > >> index 3b0e8248e1a4..07c4fb4b82b4 100644 > >> --- a/arch/arm64/include/asm/tlbflush.h > >> +++ b/arch/arm64/include/asm/tlbflush.h > >> @@ -166,7 +166,7 @@ static inline unsigned long get_trans_granule(void) > >> */ > >> #define TLBI_RANGE_MASK GENMASK_ULL(4, 0) > >> #define __TLBI_RANGE_NUM(pages, scale) \ > >> - ((((pages) >> (5 * (scale) + 1)) & TLBI_RANGE_MASK) - 1) > >> + ((((pages) >> (5 * (scale) + 1)) - 1) & TLBI_RANGE_MASK) > >> /* > >> * TLB Invalidation > > > > This looks pretty wrong, by the very definition of the comment that's > > just above: > > > > <quote> > > /* > > * Generate 'num' values from -1 to 30 with -1 rejected by the > > * __flush_tlb_range() loop below. > > */ > > </quote> > > > > With your change, num can't ever be negative, and that breaks > > __flush_tlb_range_op(): > > > > <quote> > > num = __TLBI_RANGE_NUM(pages, scale); \ > > if (num >= 0) { \ > > addr = __TLBI_VADDR_RANGE(start >> shift, asid, \ > > scale, num, tlb_level); \ > > __tlbi(r##op, addr); \ > > if (tlbi_user) \ > > __tlbi_user(r##op, addr); \ > > start += __TLBI_RANGE_PAGES(num, scale) << PAGE_SHIFT; \ > > pages -= __TLBI_RANGE_PAGES(num, scale); \ > > } \ > > scale--; \ > > </quote> > > > > We'll then shove whatever value we've found in the TLBI operation, > > leading to unknown results instead of properly adjusting the scale to > > issue a smaller invalidation. > > > > Marc, thanks for your review and comments. > > Indeed, this patch is incomplete at least. I think we need __TLBI_RANGE_NUM() > to return [-1 31] instead of [-1 30], to be consistent with MAX_TLBI_RANGE_PAGES. > -1 will be rejected in the following loop. I'm not 100% sure if I did the correct > calculation though. > > /* > * Generate 'num' values in range [-1 31], but -1 will be rejected > * by the __flush_tlb_range() loop below. > */ > #define __TLBI_RANGE_NUM(pages, scale) \ > ({ \ > int __next = (pages) & (1ULL << (5 * (scale) + 6)); \ > int __mask = ((pages) >> (5 * (scale) + 1)) & TLBI_RANGE_MASK; \ > int __num = (((pages) >> (5 * (scale) + 1)) - 1) & \ > TLBI_RANGE_MASK; \ > (__next || __mask) ? __num : -1; \ > })
I'm afraid I don't follow the logic here, and it looks awfully complex. I came up with something simpler with this:
diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h index 3b0e8248e1a4..b3f1a9c61189 100644 --- a/arch/arm64/include/asm/tlbflush.h +++ b/arch/arm64/include/asm/tlbflush.h @@ -161,12 +161,18 @@ static inline unsigned long get_trans_granule(void) #define MAX_TLBI_RANGE_PAGES __TLBI_RANGE_PAGES(31, 3) /* - * Generate 'num' values from -1 to 30 with -1 rejected by the + * Generate 'num' values from -1 to 31 with -1 rejected by the * __flush_tlb_range() loop below. */ #define TLBI_RANGE_MASK GENMASK_ULL(4, 0) -#define __TLBI_RANGE_NUM(pages, scale) \ - ((((pages) >> (5 * (scale) + 1)) & TLBI_RANGE_MASK) - 1) +#define __TLBI_RANGE_NUM(pages, scale) \ + ({ \ + int __pages = min((pages), \ + __TLBI_RANGE_PAGES(31, (scale))); \ + int __numplus1 = __pages >> (5 * (scale) + 1); \ + \ + (__numplus1 - 1); \ + }) /* * TLB Invalidation @@ -379,10 +385,6 @@ static inline void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) * 3. If there is 1 page remaining, flush it through non-range operations. Range * operations can only span an even number of pages. We save this for last to * ensure 64KB start alignment is maintained for the LPA2 case. - * - * Note that certain ranges can be represented by either num = 31 and - * scale or num = 0 and scale + 1. The loop below favours the latter - * since num is limited to 30 by the __TLBI_RANGE_NUM() macro. */ #define __flush_tlb_range_op(op, start, pages, stride, \ asid, tlb_level, tlbi_user, lpa2) \ > > Alternatively, we can also limit the number of pages to be invalidated from > arch/arm64/kvm/hyp/pgtable.c::kvm_tlb_flush_vmid_range() because the maximal > capacity is (MAX_TLBI_RANGE_PAGES - 1) instead of MAX_TLBI_RANGE_PAGES, as > the comments for __flush_tlb_range_nosync() say. > > - inval_pages = min(pages, MAX_TLBI_RANGE_PAGES); > + inval_pages = min(pages, MAX_TLBI_RANGE_PAGES - 1); > > > static inline void __flush_tlb_range_nosync(...) > { > : > /* > * When not uses TLB range ops, we can handle up to > * (MAX_DVM_OPS - 1) pages; > * When uses TLB range ops, we can handle up to > * (MAX_TLBI_RANGE_PAGES - 1) pages. > */ > if ((!system_supports_tlb_range() && > (end - start) >= (MAX_DVM_OPS * stride)) || > pages >= MAX_TLBI_RANGE_PAGES) { > flush_tlb_mm(vma->vm_mm); > return; > } > } > > Please let me know which way is better.
I would really prefer to fix the range stuff itself instead of papering over the problem by reducing the reach of the range invalidation.
> > > I think the problem is that you are triggering NUM=31 and SCALE=3, > > which the current code cannot handle as per the comment above > > __flush_tlb_range_op() (we can't do NUM=30 and SCALE=4, obviously). > > > > Yes, exactly. > > > Can you try the untested patch below? > > > > > > diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h > > index 3b0e8248e1a4..b71a1cece802 100644 > > --- a/arch/arm64/include/asm/tlbflush.h > > +++ b/arch/arm64/include/asm/tlbflush.h > > @@ -379,10 +379,6 @@ static inline void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) > > * 3. If there is 1 page remaining, flush it through non-range operations. Range > > * operations can only span an even number of pages. We save this for last to > > * ensure 64KB start alignment is maintained for the LPA2 case. > > - * > > - * Note that certain ranges can be represented by either num = 31 and > > - * scale or num = 0 and scale + 1. The loop below favours the latter > > - * since num is limited to 30 by the __TLBI_RANGE_NUM() macro. > > */ > > #define __flush_tlb_range_op(op, start, pages, stride, \ > > asid, tlb_level, tlbi_user, lpa2) \ > > @@ -407,6 +403,7 @@ do { \ > > \ > > num = __TLBI_RANGE_NUM(pages, scale); \ > > if (num >= 0) { \ > > + num += 1; \ > > addr = __TLBI_VADDR_RANGE(start >> shift, asid, \ > > scale, num, tlb_level); \ > > __tlbi(r##op, addr); \ > > > > Thanks, but I don't think it's going to work. The loop will be running infinitely > because the condition 'if (num >= 0)' can't be met when @pages is 0x200000 when > @scale is 3/2/1/0 until @scale becomes negative and positive again, but @scale > isn't in range [0 3]. I ported the chunk of code to user-space and I can see this > with added printf() messages.
Yeah, we lose num==0, which is silly. Hopefully the hack above helps a bit.
Thanks,
M.
-- Without deviation from the norm, progress is not possible.
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