[PATCH v3 24/28] KVM: SVM: Update svm->ldr_reg cache even if LDR is "bad"

From: Sean Christopherson
Date: Tue Sep 20 2022 - 19:34:04 EST


Update SVM's cache of the LDR even if the new value is "bad". Leaving
stale information in the cache can result in KVM missing updates and/or
invalidating the wrong entry, e.g. if avic_invalidate_logical_id_entry()
is triggered after a different vCPU has "claimed" the old LDR.

Fixes: 18f40c53e10f ("svm: Add VMEXIT handlers for AVIC")
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/svm/avic.c | 17 +++++++----------
1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 2b640c73f447..4b6fc9d64f4d 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -539,23 +539,24 @@ static u32 *avic_get_logical_id_entry(struct kvm_vcpu *vcpu, u32 ldr, bool flat)
return &logical_apic_id_table[index];
}

-static int avic_ldr_write(struct kvm_vcpu *vcpu, u8 g_physical_id, u32 ldr)
+static void avic_ldr_write(struct kvm_vcpu *vcpu, u8 g_physical_id, u32 ldr)
{
bool flat;
u32 *entry, new_entry;

+ if (!ldr)
+ return;
+
flat = kvm_lapic_get_reg(vcpu->arch.apic, APIC_DFR) == APIC_DFR_FLAT;
entry = avic_get_logical_id_entry(vcpu, ldr, flat);
if (!entry)
- return -EINVAL;
+ return;

new_entry = READ_ONCE(*entry);
new_entry &= ~AVIC_LOGICAL_ID_ENTRY_GUEST_PHYSICAL_ID_MASK;
new_entry |= (g_physical_id & AVIC_LOGICAL_ID_ENTRY_GUEST_PHYSICAL_ID_MASK);
new_entry |= AVIC_LOGICAL_ID_ENTRY_VALID_MASK;
WRITE_ONCE(*entry, new_entry);
-
- return 0;
}

static void avic_invalidate_logical_id_entry(struct kvm_vcpu *vcpu)
@@ -575,7 +576,6 @@ static void avic_invalidate_logical_id_entry(struct kvm_vcpu *vcpu)

static void avic_handle_ldr_update(struct kvm_vcpu *vcpu)
{
- int ret = 0;
struct vcpu_svm *svm = to_svm(vcpu);
u32 ldr = kvm_lapic_get_reg(vcpu->arch.apic, APIC_LDR);
u32 id = kvm_xapic_id(vcpu->arch.apic);
@@ -589,11 +589,8 @@ static void avic_handle_ldr_update(struct kvm_vcpu *vcpu)

avic_invalidate_logical_id_entry(vcpu);

- if (ldr)
- ret = avic_ldr_write(vcpu, id, ldr);
-
- if (!ret)
- svm->ldr_reg = ldr;
+ svm->ldr_reg = ldr;
+ avic_ldr_write(vcpu, id, ldr);
}

static void avic_handle_dfr_update(struct kvm_vcpu *vcpu)
--
2.37.3.968.ga6b4b080e4-goog