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KVM: x86/mmu: Yield in TDU MMU iter even if no SPTES changed

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Given certain conditions, some TDP MMU functions may not yield
reliably / frequently enough. For example, if a paging structure was
very large but had few, if any writable entries, wrprot_gfn_range
could traverse many entries before finding a writable entry and yielding
because the check for yielding only happens after an SPTE is modified.

Fix this issue by moving the yield to the beginning of the loop.

Fixes: a6a0b05da9f3 ("kvm: x86/mmu: Support dirty logging for the TDP MMU")
Reviewed-by: Peter Feiner <pfeiner@google.com>
Signed-off-by: Ben Gardon <bgardon@google.com>

Message-Id: <20210202185734.1680553-15-bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Ben Gardon 2021-02-02 10:57:20 -08:00 committed by Paolo Bonzini
parent ed5e484b79
commit 1af4a96025
1 changed files with 22 additions and 10 deletions
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32
arch/x86/kvm/mmu/tdp_mmu.c
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@ -501,6 +501,12 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
bool flush_needed = false;
tdp_root_for_each_pte(iter, root, start, end) {
if (can_yield &&
tdp_mmu_iter_cond_resched(kvm, &iter, flush_needed)) {
flush_needed = false;
continue;
}
if (!is_shadow_present_pte(iter.old_spte))
continue;
@ -515,9 +521,7 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
continue;
tdp_mmu_set_spte(kvm, &iter, 0);
flush_needed = !(can_yield &&
tdp_mmu_iter_cond_resched(kvm, &iter, true));
flush_needed = true;
}
return flush_needed;
}
@ -880,6 +884,9 @@ static bool wrprot_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
for_each_tdp_pte_min_level(iter, root->spt, root->role.level,
min_level, start, end) {
if (tdp_mmu_iter_cond_resched(kvm, &iter, false))
continue;
if (!is_shadow_present_pte(iter.old_spte) ||
!is_last_spte(iter.old_spte, iter.level))
continue;
@ -888,8 +895,6 @@ static bool wrprot_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
tdp_mmu_set_spte_no_dirty_log(kvm, &iter, new_spte);
spte_set = true;
tdp_mmu_iter_cond_resched(kvm, &iter, false);
}
return spte_set;
}
@ -933,6 +938,9 @@ static bool clear_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
bool spte_set = false;
tdp_root_for_each_leaf_pte(iter, root, start, end) {
if (tdp_mmu_iter_cond_resched(kvm, &iter, false))
continue;
if (spte_ad_need_write_protect(iter.old_spte)) {
if (is_writable_pte(iter.old_spte))
new_spte = iter.old_spte & ~PT_WRITABLE_MASK;
@ -947,8 +955,6 @@ static bool clear_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
tdp_mmu_set_spte_no_dirty_log(kvm, &iter, new_spte);
spte_set = true;
tdp_mmu_iter_cond_resched(kvm, &iter, false);
}
return spte_set;
}
@ -1056,6 +1062,9 @@ static bool set_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
bool spte_set = false;
tdp_root_for_each_pte(iter, root, start, end) {
if (tdp_mmu_iter_cond_resched(kvm, &iter, false))
continue;
if (!is_shadow_present_pte(iter.old_spte))
continue;
@ -1063,8 +1072,6 @@ static bool set_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
tdp_mmu_set_spte(kvm, &iter, new_spte);
spte_set = true;
tdp_mmu_iter_cond_resched(kvm, &iter, false);
}
return spte_set;
@ -1105,6 +1112,11 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
bool spte_set = false;
tdp_root_for_each_pte(iter, root, start, end) {
if (tdp_mmu_iter_cond_resched(kvm, &iter, spte_set)) {
spte_set = false;
continue;
}
if (!is_shadow_present_pte(iter.old_spte) ||
!is_last_spte(iter.old_spte, iter.level))
continue;
@ -1116,7 +1128,7 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
tdp_mmu_set_spte(kvm, &iter, 0);
spte_set = !tdp_mmu_iter_cond_resched(kvm, &iter, true);
spte_set = true;
}
if (spte_set)