[PATCH 2/7] KVM: x86: Invoke kvm_mmu_unload() directly on CR4.PCIDE change

Sean Christopherson
2021-12-09T06:06:06Z

Replace a KVM_REQ_MMU_RELOAD request with a direct kvm_mmu_unload() call
when the guest's CR4.PCIDE changes. This will allow tweaking the logic
of KVM_REQ_MMU_RELOAD to free only obsolete/invalid roots, which is the
historical intent of KVM_REQ_MMU_RELOAD. The recent PCIDE behavior is
the only user of KVM_REQ_MMU_RELOAD that doesn't mark affected roots as
obsolete, needs to unconditionally unload the entire MMU, _and_ affects
only the current vCPU.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/x86.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1aaf37e1bd0f..ca1f0350a868 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1045,19 +1045,18 @@ void kvm_post_set_cr4(struct kvm_vcpu *vcpu, unsigned long old_cr4, unsigned lon
* If CR4.PCIDE is changed 0 -> 1, there is no need to flush the TLB
* according to the SDM; however, stale prev_roots could be reused
* incorrectly in the future after a MOV to CR3 with NOFLUSH=1, so we
- * free them all. KVM_REQ_MMU_RELOAD is fit for the both cases; it
- * is slow, but changing CR4.PCIDE is a rare case.
+ * free them all. kvm_mmu_unload() is fit for the both cases; it is
+ * slow, but changing CR4.PCIDE is a rare case.
*
* If CR4.PGE is changed, the guest TLB must be flushed.
*
- * Note: resetting MMU is a superset of KVM_REQ_MMU_RELOAD and
- * KVM_REQ_MMU_RELOAD is a superset of KVM_REQ_TLB_FLUSH_GUEST, hence
- * the usage of "else if".
+ * Note: resetting MMU is a superset of unloading an MMU, and unloading
+ * an MMU is a superset of KVM_REQ_TLB_FLUSH_GUEST, hence the "else if".
*/
if ((cr4 ^ old_cr4) & KVM_MMU_CR4_ROLE_BITS)
kvm_mmu_reset_context(vcpu);
else if ((cr4 ^ old_cr4) & X86_CR4_PCIDE)
- kvm_make_request(KVM_REQ_MMU_RELOAD, vcpu);
+ kvm_mmu_unload(vcpu);
else if ((cr4 ^ old_cr4) & X86_CR4_PGE)
kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu);
}
--
2.34.1.400.ga245620fadb-goog