[PATCH 5.11 109/152] KVM: x86/mmu: Yield in TDU MMU iter even if no SPTES changed

Greg Kroah-Hartman
2021-04-05T09:23:23Z

From: Ben Gardon <bgardon@google.com>

[ Upstream commit 1af4a96025b33587ca953c7ef12a1b20c6e70412 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/kvm/mmu/tdp_mmu.c | 32 ++++++++++++++++++++++----------
1 file changed, 22 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index a07d37abb63f..0567286fba39 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -470,6 +470,12 @@ 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;

@@ -484,9 +490,7 @@ 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;
}
@@ -850,6 +854,9 @@ 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;
@@ -858,8 +865,6 @@ 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;
}
@@ -903,6 +908,9 @@ 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;
@@ -917,8 +925,6 @@ 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;
}
@@ -1026,6 +1032,9 @@ 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;

@@ -1033,8 +1042,6 @@ 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;
@@ -1075,6 +1082,11 @@ 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;
@@ -1087,7 +1099,7 @@ 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)
--
2.30.1