mirrors/linux
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2026-04-29 05:52:38 -04:00
Code Issues Packages Projects Releases Wiki Activity

KVM: x86/mmu: Avoid unnecessary flush on eager page split

Browse Source 
The TLB flush before installing the newly-populated lower level
page table is unnecessary if the lower-level page table maps
the huge page identically.  KVM knows it is if it did not reuse
an existing shadow page table, tell drop_large_spte() to skip
the flush in that case.

Extracted from a patch by David Matlack.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini
2022-06-22 15:27:10 -04:00
parent ada51a9de7
commit 0378739401
1 changed files with 20 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files

32
arch/x86/kvm/mmu/mmu.c
View File

@@ -1135,7 +1135,7 @@ static void drop_spte(struct kvm *kvm, u64 *sptep)
rmap_remove(kvm, sptep);
}
static void drop_large_spte(struct kvm *kvm, u64 *sptep)
static void drop_large_spte(struct kvm *kvm, u64 *sptep, bool flush)
{
struct kvm_mmu_page *sp;
@@ -1143,7 +1143,9 @@ static void drop_large_spte(struct kvm *kvm, u64 *sptep)
WARN_ON(sp->role.level == PG_LEVEL_4K);
drop_spte(kvm, sptep);
kvm_flush_remote_tlbs_with_address(kvm, sp->gfn,
if (flush)
kvm_flush_remote_tlbs_with_address(kvm, sp->gfn,
KVM_PAGES_PER_HPAGE(sp->role.level));
}
@@ -2283,7 +2285,7 @@ static void shadow_walk_next(struct kvm_shadow_walk_iterator *iterator)
static void __link_shadow_page(struct kvm *kvm,
struct kvm_mmu_memory_cache *cache, u64 *sptep,
struct kvm_mmu_page *sp)
struct kvm_mmu_page *sp, bool flush)
{
u64 spte;
@@ -2291,10 +2293,11 @@ static void __link_shadow_page(struct kvm *kvm,
/*
* If an SPTE is present already, it must be a leaf and therefore
* a large one. Drop it and flush the TLB before installing sp.
* a large one. Drop it, and flush the TLB if needed, before
* installing sp.
*/
if (is_shadow_present_pte(*sptep))
drop_large_spte(kvm, sptep);
drop_large_spte(kvm, sptep, flush);
spte = make_nonleaf_spte(sp->spt, sp_ad_disabled(sp));
@@ -2309,7 +2312,7 @@ static void __link_shadow_page(struct kvm *kvm,
static void link_shadow_page(struct kvm_vcpu *vcpu, u64 *sptep,
struct kvm_mmu_page *sp)
{
__link_shadow_page(vcpu->kvm, &vcpu->arch.mmu_pte_list_desc_cache, sptep, sp);
__link_shadow_page(vcpu->kvm, &vcpu->arch.mmu_pte_list_desc_cache, sptep, sp, true);
}
static void validate_direct_spte(struct kvm_vcpu *vcpu, u64 *sptep,
@@ -6170,6 +6173,7 @@ static void shadow_mmu_split_huge_page(struct kvm *kvm,
struct kvm_mmu_memory_cache *cache = &kvm->arch.split_desc_cache;
u64 huge_spte = READ_ONCE(*huge_sptep);
struct kvm_mmu_page *sp;
bool flush = false;
u64 *sptep, spte;
gfn_t gfn;
int index;
@@ -6187,20 +6191,24 @@ static void shadow_mmu_split_huge_page(struct kvm *kvm,
* gfn-to-pfn translation since the SP is direct, so no need to
* modify them.
*
* If a given SPTE points to a lower level page table, installing
* such SPTEs would effectively unmap a potion of the huge page.
* This is not an issue because __link_shadow_page() flushes the TLB
* when the passed sp replaces a large SPTE.
* However, if a given SPTE points to a lower level page table,
* that lower level page table may only be partially populated.
* Installing such SPTEs would effectively unmap a potion of the
* huge page. Unmapping guest memory always requires a TLB flush
* since a subsequent operation on the unmapped regions would
* fail to detect the need to flush.
*/
if (is_shadow_present_pte(*sptep))
if (is_shadow_present_pte(*sptep)) {
flush |= !is_last_spte(*sptep, sp->role.level);
continue;
}
spte = make_huge_page_split_spte(kvm, huge_spte, sp->role, index);
mmu_spte_set(sptep, spte);
__rmap_add(kvm, cache, slot, sptep, gfn, sp->role.access);
}
__link_shadow_page(kvm, cache, huge_sptep, sp);
__link_shadow_page(kvm, cache, huge_sptep, sp, flush);
}
static int shadow_mmu_try_split_huge_page(struct kvm *kvm,