[PATCH 8/9] KVM: x86: When guest set CR3, handle LAM bits semantics

Robert Hoo
2022-10-17T07:05:52Z

When only changes LAM bits, ask next vcpu run to load mmu pgd, so that it
will build new CR3 with LAM bits updates. No TLB flush needed on this case.
When changes on effective addresses, no matter LAM bits changes or not, go
through normal pgd update process.

Signed-off-by: Robert Hoo <robert.hu@linux.intel.com>
---
arch/x86/kvm/x86.c | 26 ++++++++++++++++++++++----
1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e9b465bff8d3..fb779f88ae88 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1228,9 +1228,9 @@ static bool kvm_is_valid_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
{
bool skip_tlb_flush = false;
- unsigned long pcid = 0;
+ unsigned long pcid = 0, old_cr3;
#ifdef CONFIG_X86_64
- bool pcid_enabled = kvm_read_cr4_bits(vcpu, X86_CR4_PCIDE);
+ bool pcid_enabled = !!kvm_read_cr4_bits(vcpu, X86_CR4_PCIDE);

if (pcid_enabled) {
skip_tlb_flush = cr3 & X86_CR3_PCID_NOFLUSH;
@@ -1243,6 +1243,10 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
if (cr3 == kvm_read_cr3(vcpu) && !is_pae_paging(vcpu))
goto handle_tlb_flush;

+ if (!guest_cpuid_has(vcpu, X86_FEATURE_LAM) &&
+ (cr3 & (X86_CR3_LAM_U48 | X86_CR3_LAM_U57)))
+ return 1;
+
/*
* Do not condition the GPA check on long mode, this helper is used to
* stuff CR3, e.g. for RSM emulation, and there is no guarantee that
@@ -1254,8 +1258,22 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
if (is_pae_paging(vcpu) && !load_pdptrs(vcpu, cr3))
return 1;

- if (cr3 != kvm_read_cr3(vcpu))
- kvm_mmu_new_pgd(vcpu, cr3);
+ old_cr3 = kvm_read_cr3(vcpu);
+ if (cr3 != old_cr3) {
+ if ((cr3 ^ old_cr3) & CR3_ADDR_MASK) {
+ kvm_mmu_new_pgd(vcpu, cr3 & ~(X86_CR3_LAM_U48 |
+ X86_CR3_LAM_U57));
+ } else {
+ /* Only LAM conf changes, no tlb flush needed */
+ skip_tlb_flush = true;
+ /*
+ * Though effective addr no change, mark the
+ * request so that LAM bits will take effect
+ * when enter guest.
+ */
+ kvm_make_request(KVM_REQ_LOAD_MMU_PGD, vcpu);
+ }
+ }

vcpu->arch.cr3 = cr3;
kvm_register_mark_dirty(vcpu, VCPU_EXREG_CR3);
--
2.31.1