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mm/hugetlb_vmemmap: don't synchronize_rcu() without HVO

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hugetlb_vmemmap_optimize_folio() and hugetlb_vmemmap_restore_folio() are
wrappers meant to be called regardless of whether HVO is enabled. 
Therefore, they should not call synchronize_rcu().  Otherwise, it
regresses use cases not enabling HVO.

So move synchronize_rcu() to __hugetlb_vmemmap_optimize_folio() and
__hugetlb_vmemmap_restore_folio(), and call it once for each batch of
folios when HVO is enabled.

Link: https://lkml.kernel.org/r/20240719042503.2752316-1-yuzhao@google.com
Fixes: bd225530a4 ("mm/hugetlb_vmemmap: fix race with speculative PFN walkers")
Signed-off-by: Yu Zhao <yuzhao@google.com>
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202407091001.1250ad4a-oliver.sang@intel.com
Reported-by: Janosch Frank <frankja@linux.ibm.com>
Tested-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Acked-by: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Yu Zhao 2024-07-18 22:25:03 -06:00 committed by Andrew Morton
parent 9eace7e8e6
commit c2a967f6ab
1 changed files with 20 additions and 20 deletions
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40
mm/hugetlb_vmemmap.c
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@ -43,6 +43,8 @@ struct vmemmap_remap_walk {
#define VMEMMAP_SPLIT_NO_TLB_FLUSH BIT(0)
/* Skip the TLB flush when we remap the PTE */
#define VMEMMAP_REMAP_NO_TLB_FLUSH BIT(1)
/* synchronize_rcu() to avoid writes from page_ref_add_unless() */
#define VMEMMAP_SYNCHRONIZE_RCU BIT(2)
unsigned long flags;
};
@ -457,6 +459,9 @@ static int __hugetlb_vmemmap_restore_folio(const struct hstate *h,
if (!folio_test_hugetlb_vmemmap_optimized(folio))
return 0;
if (flags & VMEMMAP_SYNCHRONIZE_RCU)
synchronize_rcu();
vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);
vmemmap_reuse = vmemmap_start;
vmemmap_start += HUGETLB_VMEMMAP_RESERVE_SIZE;
@ -489,10 +494,7 @@ static int __hugetlb_vmemmap_restore_folio(const struct hstate *h,
*/
int hugetlb_vmemmap_restore_folio(const struct hstate *h, struct folio *folio)
{
/* avoid writes from page_ref_add_unless() while unfolding vmemmap */
synchronize_rcu();
return __hugetlb_vmemmap_restore_folio(h, folio, 0);
return __hugetlb_vmemmap_restore_folio(h, folio, VMEMMAP_SYNCHRONIZE_RCU);
}
/**
@ -515,14 +517,14 @@ long hugetlb_vmemmap_restore_folios(const struct hstate *h,
struct folio *folio, *t_folio;
long restored = 0;
long ret = 0;
/* avoid writes from page_ref_add_unless() while unfolding vmemmap */
synchronize_rcu();
unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH | VMEMMAP_SYNCHRONIZE_RCU;
list_for_each_entry_safe(folio, t_folio, folio_list, lru) {
if (folio_test_hugetlb_vmemmap_optimized(folio)) {
ret = __hugetlb_vmemmap_restore_folio(h, folio,
VMEMMAP_REMAP_NO_TLB_FLUSH);
ret = __hugetlb_vmemmap_restore_folio(h, folio, flags);
/* only need to synchronize_rcu() once for each batch */
flags &= ~VMEMMAP_SYNCHRONIZE_RCU;
if (ret)
break;
restored++;
@ -570,6 +572,9 @@ static int __hugetlb_vmemmap_optimize_folio(const struct hstate *h,
return ret;
static_branch_inc(&hugetlb_optimize_vmemmap_key);
if (flags & VMEMMAP_SYNCHRONIZE_RCU)
synchronize_rcu();
/*
* Very Subtle
* If VMEMMAP_REMAP_NO_TLB_FLUSH is set, TLB flushing is not performed
@ -617,10 +622,7 @@ void hugetlb_vmemmap_optimize_folio(const struct hstate *h, struct folio *folio)
{
LIST_HEAD(vmemmap_pages);
/* avoid writes from page_ref_add_unless() while folding vmemmap */
synchronize_rcu();
__hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, 0);
__hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, VMEMMAP_SYNCHRONIZE_RCU);
free_vmemmap_page_list(&vmemmap_pages);
}
@ -647,6 +649,7 @@ void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_l
{
struct folio *folio;
LIST_HEAD(vmemmap_pages);
unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH | VMEMMAP_SYNCHRONIZE_RCU;
list_for_each_entry(folio, folio_list, lru) {
int ret = hugetlb_vmemmap_split_folio(h, folio);
@ -663,14 +666,12 @@ void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_l
flush_tlb_all();
/* avoid writes from page_ref_add_unless() while folding vmemmap */
synchronize_rcu();
list_for_each_entry(folio, folio_list, lru) {
int ret;
ret = __hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages,
VMEMMAP_REMAP_NO_TLB_FLUSH);
ret = __hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, flags);
/* only need to synchronize_rcu() once for each batch */
flags &= ~VMEMMAP_SYNCHRONIZE_RCU;
/*
* Pages to be freed may have been accumulated. If we
@ -684,8 +685,7 @@ void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_l
flush_tlb_all();
free_vmemmap_page_list(&vmemmap_pages);
INIT_LIST_HEAD(&vmemmap_pages);
__hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages,
VMEMMAP_REMAP_NO_TLB_FLUSH);
__hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, flags);
}
}