[PATCH v13 50/85] KVM: VMX: Hold mmu_lock until page is released when updating APIC access page

Sean Christopherson
2024-10-10T19:22:28Z

Hold mmu_lock across kvm_release_pfn_clean() when refreshing the APIC
access page address to ensure that KVM doesn't mark a page/folio as
accessed after it has been unmapped. Practically speaking marking a folio
accesses is benign in this scenario, as KVM does hold a reference (it's
really just marking folios dirty that is problematic), but there's no
reason not to be paranoid (moving the APIC access page isn't a hot path),
and no reason to be different from other mmu_notifier-protected flows in
KVM.

Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/vmx/vmx.c | 21 +++++++++------------
1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 1a4438358c5e..851be0820e04 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6832,25 +6832,22 @@ void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu)
return;

read_lock(&vcpu->kvm->mmu_lock);
- if (mmu_invalidate_retry_gfn(kvm, mmu_seq, gfn)) {
+ if (mmu_invalidate_retry_gfn(kvm, mmu_seq, gfn))
kvm_make_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu);
- read_unlock(&vcpu->kvm->mmu_lock);
- goto out;
- }
+ else
+ vmcs_write64(APIC_ACCESS_ADDR, pfn_to_hpa(pfn));

- vmcs_write64(APIC_ACCESS_ADDR, pfn_to_hpa(pfn));
- read_unlock(&vcpu->kvm->mmu_lock);
-
- /*
- * No need for a manual TLB flush at this point, KVM has already done a
- * flush if there were SPTEs pointing at the previous page.
- */
-out:
/*
* Do not pin apic access page in memory, the MMU notifier
* will call us again if it is migrated or swapped out.
*/
kvm_release_pfn_clean(pfn);
+
+ /*
+ * No need for a manual TLB flush at this point, KVM has already done a
+ * flush if there were SPTEs pointing at the previous page.
+ */
+ read_unlock(&vcpu->kvm->mmu_lock);
}

void vmx_hwapic_isr_update(int max_isr)