The following commit has been merged into the x86/mm branch of tip:
Commit-ID: 8f1d56f64f8d6b80dea2d1978d10071132a695c5
Gitweb: https://git.kernel.org/tip/8f1d56f64f8d6b80dea2d1978d10071132a695c5
Author: Nadav Amit <namit@xxxxxxxxxx>
AuthorDate: Sun, 10 Jul 2022 16:28:37 -07:00
Committer: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
CommitterDate: Tue, 19 Jul 2022 09:04:52 -07:00
x86/mm/tlb: Ignore f->new_tlb_gen when zero
Commit aa44284960d5 ("x86/mm/tlb: Avoid reading mm_tlb_gen when
possible") introduced an optimization to skip superfluous TLB
flushes based on the generation provided in flush_tlb_info.
However, arch_tlbbatch_flush() does not provide any generation in
flush_tlb_info and populates the flush_tlb_info generation with
0. This 0 is causes the flush_tlb_info to be interpreted as a
superfluous, old flush. As a result, try_to_unmap_one() would
not perform any TLB flushes.
Fix it by checking whether f->new_tlb_gen is nonzero. Zero value
is anyhow is an invalid generation value. To avoid future
confusion, introduce TLB_GENERATION_INVALID constant and use it
properly. Add warnings to ensure no partial flushes are done with
TLB_GENERATION_INVALID or when f->mm is NULL, since this does not
make any sense.
In addition, add the missing unlikely().
[ dhansen: change VM_BUG_ON() -> VM_WARN_ON(), clarify changelog ]
Fixes: aa44284960d5 ("x86/mm/tlb: Avoid reading mm_tlb_gen when possible")
Reported-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Tested-by: Hugh Dickins <hughd@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20220710232837.3618-1-namit@xxxxxxxxxx
---
arch/x86/include/asm/tlbflush.h | 1 +
arch/x86/mm/tlb.c | 15 ++++++++++++---
2 files changed, 13 insertions(+), 3 deletions(-)
diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 98fa0a1..21bf105 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -16,6 +16,7 @@
void __flush_tlb_all(void);
#define TLB_FLUSH_ALL -1UL
+#define TLB_GENERATION_INVALID 0
void cr4_update_irqsoff(unsigned long set, unsigned long clear);
unsigned long cr4_read_shadow(void);
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index d9314cc..c1e31e9 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -771,7 +771,8 @@ static void flush_tlb_func(void *info)
return;
}
- if (f->new_tlb_gen <= local_tlb_gen) {
+ if (unlikely(f->new_tlb_gen != TLB_GENERATION_INVALID &&
+ f->new_tlb_gen <= local_tlb_gen)) {
/*
* The TLB is already up to date in respect to f->new_tlb_gen.
* While the core might be still behind mm_tlb_gen, checking
@@ -843,6 +844,12 @@ static void flush_tlb_func(void *info)
/* Partial flush */
unsigned long addr = f->start;
+ /* Partial flush cannot have invalid generations */
+ VM_WARN_ON(f->new_tlb_gen == TLB_GENERATION_INVALID);
+
+ /* Partial flush must have valid mm */
+ VM_WARN_ON(f->mm == NULL);
+
nr_invalidate = (f->end - f->start) >> f->stride_shift;
while (addr < f->end) {
@@ -1045,7 +1052,8 @@ void flush_tlb_kernel_range(unsigned long start, unsigned long end)
struct flush_tlb_info *info;
preempt_disable();
- info = get_flush_tlb_info(NULL, start, end, 0, false, 0);
+ info = get_flush_tlb_info(NULL, start, end, 0, false,
+ TLB_GENERATION_INVALID);
on_each_cpu(do_kernel_range_flush, info, 1);
@@ -1214,7 +1222,8 @@ 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, 0);
+ info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, 0, false,
+ TLB_GENERATION_INVALID);
/*
* flush_tlb_multi() is not optimized for the common case in which only
* a local TLB flush is needed. Optimize this use-case by calling
|