| Message ID | 20250206044346.3810242-4-riel@surriel.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | AMD broadcast TLB invalidation | expand |
On Thu, 6 Feb 2025 at 05:45, Rik van Riel <riel@surriel.com> wrote: > @@ -1276,7 +1282,7 @@ void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) > > int cpu = get_cpu(); > > - info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, 0, false, > + info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, PAGE_SHIFT, false, > TLB_GENERATION_INVALID); [Why] do we need this change? If it's necessary here, why isn't it needed everywhere else that does TLB_FLUSH_ALL too, like flush_tlb_mm()?
On Fri, 2025-02-07 at 15:50 +0100, Brendan Jackman wrote: > On Thu, 6 Feb 2025 at 05:45, Rik van Riel <riel@surriel.com> wrote: > > @@ -1276,7 +1282,7 @@ void arch_tlbbatch_flush(struct > > arch_tlbflush_unmap_batch *batch) > > > > int cpu = get_cpu(); > > > > - info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, 0, false, > > + info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, > > PAGE_SHIFT, false, > > TLB_GENERATION_INVALID); > > [Why] do we need this change? If it's necessary here, why isn't it > needed everywhere else that does TLB_FLUSH_ALL too, like > flush_tlb_mm()? > flush_tlb_mm() calls flush_tlb_mm_range(), which does also use get_flush_tlb_info(). We pass in PAGE_SHIFT here to ensure that the stride shift is specified correctly to the INVLPGB instruction later on.
On Fri, 7 Feb 2025 at 21:25, Rik van Riel <riel@surriel.com> wrote: > > On Fri, 2025-02-07 at 15:50 +0100, Brendan Jackman wrote: > > On Thu, 6 Feb 2025 at 05:45, Rik van Riel <riel@surriel.com> wrote: > > > @@ -1276,7 +1282,7 @@ void arch_tlbbatch_flush(struct > > > arch_tlbflush_unmap_batch *batch) > > > > > > int cpu = get_cpu(); > > > > > > - info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, 0, false, > > > + info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, > > > PAGE_SHIFT, false, > > > TLB_GENERATION_INVALID); > > > > [Why] do we need this change? If it's necessary here, why isn't it > > needed everywhere else that does TLB_FLUSH_ALL too, like > > flush_tlb_mm()? > > > flush_tlb_mm() calls flush_tlb_mm_range(), which > does also use get_flush_tlb_info(). > > We pass in PAGE_SHIFT here to ensure that the > stride shift is specified correctly to the > INVLPGB instruction later on. Hm I don't follow your answer here so lemme just state my current understanding more verbosely... flush_tlb_mm() indirectly calls get_flush_tlb_info() with end=TLB_FLUSH_ALL and stride_shift=0. That's an invalid stride shift, but this doesn't break anything because with TLB_FLUSH_ALL the stride shift is never used (except to check for values above PMD_SHIFT). So here I think passing stride_shift=0 would be fine too. Concretely, here we specifically call invlpgb_flush_all_nonglobals() which doesn't care about stride_shift, and flush_tlb_func() is the same as before this patchset in this respect. I would be quite happy with removing the "it's invalid but it doesn't matter" thing everywhere but this seems to be localised and I think the issue is orthogonal to the presence of invlpgb.
On Fri, 2025-02-07 at 15:50 +0100, Brendan Jackman wrote: > On Thu, 6 Feb 2025 at 05:45, Rik van Riel <riel@surriel.com> wrote: > > @@ -1276,7 +1282,7 @@ void arch_tlbbatch_flush(struct > > arch_tlbflush_unmap_batch *batch) > > > > int cpu = get_cpu(); > > > > - info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, 0, false, > > + info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, > > PAGE_SHIFT, false, > > TLB_GENERATION_INVALID); > > [Why] do we need this change? If it's necessary here, why isn't it > needed everywhere else that does TLB_FLUSH_ALL too, like > flush_tlb_mm()? > You are right, we do not actually need this. I'll drop this for v10
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 6cf881a942bb..36939b104561 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -1000,8 +1000,13 @@ static struct flush_tlb_info *get_flush_tlb_info(struct mm_struct *mm, BUG_ON(this_cpu_inc_return(flush_tlb_info_idx) != 1); #endif - info->start = start; - info->end = end; + /* + * Round the start and end addresses to the page size specified + * by the stride shift. This ensures partial pages at the end of + * a range get fully invalidated. + */ + info->start = round_down(start, 1 << stride_shift); + info->end = round_up(end, 1 << stride_shift); info->mm = mm; info->stride_shift = stride_shift; info->freed_tables = freed_tables; @@ -1009,6 +1014,19 @@ static struct flush_tlb_info *get_flush_tlb_info(struct mm_struct *mm, info->initiating_cpu = smp_processor_id(); info->trim_cpumask = 0; + WARN_ONCE(start != info->start || end != info->end, + "TLB flush not stride %x aligned. Start %lx, end %lx\n", + 1 << stride_shift, start, end); + + /* + * If the number of flushes is so large that a full flush + * would be faster, do a full flush. + */ + if ((end - start) >> stride_shift > tlb_single_page_flush_ceiling) { + info->start = 0; + info->end = TLB_FLUSH_ALL; + } + return info; } @@ -1026,17 +1044,8 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start, bool freed_tables) { struct flush_tlb_info *info; + int cpu = get_cpu(); u64 new_tlb_gen; - int cpu; - - cpu = get_cpu(); - - /* Should we flush just the requested range? */ - if ((end == TLB_FLUSH_ALL) || - ((end - start) >> stride_shift) > tlb_single_page_flush_ceiling) { - start = 0; - end = TLB_FLUSH_ALL; - } /* This is also a barrier that synchronizes with switch_mm(). */ new_tlb_gen = inc_mm_tlb_gen(mm); @@ -1089,22 +1098,19 @@ static void do_kernel_range_flush(void *info) void flush_tlb_kernel_range(unsigned long start, unsigned long end) { - /* Balance as user space task's flush, a bit conservative */ - if (end == TLB_FLUSH_ALL || - (end - start) > tlb_single_page_flush_ceiling << PAGE_SHIFT) { - on_each_cpu(do_flush_tlb_all, NULL, 1); - } else { - struct flush_tlb_info *info; + struct flush_tlb_info *info; - preempt_disable(); - info = get_flush_tlb_info(NULL, start, end, 0, false, - TLB_GENERATION_INVALID); + guard(preempt)(); + + info = get_flush_tlb_info(NULL, start, end, PAGE_SHIFT, false, + TLB_GENERATION_INVALID); + if (info->end == TLB_FLUSH_ALL) + on_each_cpu(do_flush_tlb_all, NULL, 1); + else on_each_cpu(do_kernel_range_flush, info, 1); - put_flush_tlb_info(); - preempt_enable(); - } + put_flush_tlb_info(); } /* @@ -1276,7 +1282,7 @@ void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) int cpu = get_cpu(); - info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, 0, false, + info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, PAGE_SHIFT, false, TLB_GENERATION_INVALID); /* * flush_tlb_multi() is not optimized for the common case in which only
Reduce code duplication by consolidating the decision point for whether to do individual invalidations or a full flush inside get_flush_tlb_info. Signed-off-by: Rik van Riel <riel@surriel.com> Suggested-by: Dave Hansen <dave.hansen@intel.com> --- arch/x86/mm/tlb.c | 56 ++++++++++++++++++++++++++--------------------- 1 file changed, 31 insertions(+), 25 deletions(-)