[PATCH] KVM: x86/mmu: Respect user goal_nr_mmu_pages after zapping oldest pages

[PATCH] KVM: x86/mmu: Respect user goal_nr_mmu_pages after zapping oldest pages

[fuqiang wang]

When kvm_mmu_change_mmu_pages() shrinks the shadow page limit and the
current number of shadow pages exceeds the requested goal, it zaps the
oldest MMU pages and then updates n_max_mmu_pages.

Previously the new limit was set unconditionally to the current
mmu_shadow_pages value observed after zapping. However, zapping can
reduce mmu_shadow_pages below the user-requested goal_nr_mmu_pages,
since a single __kvm_mmu_prepare_zap_page() may reclaim more than one
MMU page (it also zaps unsync/child pages). This could then clamp the
limit below the user's intent.

Use max(mmu_shadow_pages, goal_nr_mmu_pages) so the user-requested goal
is honored even if zapping overshoots.

Signed-off-by: fuqiang wang <fuqiang.wng@gmail.com>
---
 arch/x86/kvm/mmu/mmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 064ecc33b926..efeba58936a6 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2913,7 +2913,7 @@ void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned long goal_nr_mmu_pages)
 		kvm_mmu_zap_oldest_mmu_pages(kvm, kvm->stat.mmu_shadow_pages -
 						  goal_nr_mmu_pages);
 
-		goal_nr_mmu_pages = kvm->stat.mmu_shadow_pages;
+		goal_nr_mmu_pages = max(kvm->stat.mmu_shadow_pages, goal_nr_mmu_pages);
 	}
 
 	kvm->arch.n_max_mmu_pages = goal_nr_mmu_pages;
-- 
2.47.0