KVM: x86: Get active PCID only when writing a CR3 value

Retrieve the active PCID only when writing a guest CR3 value, i.e. don't
get the PCID when using EPT or NPT.  The PCID is especially problematic
for EPT as the bits have different meaning, and so the PCID and must be
manually stripped, which is annoying and unnecessary.  And on VMX,
getting the active PCID also involves reading the guest's CR3 and
CR4.PCIDE, i.e. may add pointless VMREADs.

Opportunistically rename the pgd/pgd_level params to root_hpa and
root_level to better reflect their new roles.  Keep the function names,
as "load the guest PGD" is still accurate/correct.

Last, and probably least, pass root_hpa as a hpa_t/u64 instead of an
unsigned long.  The EPTP holds a 64-bit value, even in 32-bit mode, so
in theory EPT could support HIGHMEM for 32-bit KVM.  Never mind that
doing so would require changing the MMU page allocators and reworking
the MMU to use kmap().

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210305183123.3978098-2-seanjc@google.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 9 insertions, 3 deletions

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 13205e9cb666..58f4dc0e7864 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3901,21 +3901,27 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
 	return svm_exit_handlers_fastpath(vcpu);
 }
 
-static void svm_load_mmu_pgd(struct kvm_vcpu *vcpu, unsigned long root,
+static void svm_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa,
 			     int root_level)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 	unsigned long cr3;
 
-	cr3 = __sme_set(root);
+	root_hpa = __sme_set(root_hpa);
 	if (npt_enabled) {
-		svm->vmcb->control.nested_cr3 = cr3;
+		svm->vmcb->control.nested_cr3 = root_hpa;
 		vmcb_mark_dirty(svm->vmcb, VMCB_NPT);
 
 		/* Loading L2's CR3 is handled by enter_svm_guest_mode.  */
 		if (!test_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail))
 			return;
 		cr3 = vcpu->arch.cr3;
+	} else if (vcpu->arch.mmu->shadow_root_level >= PT64_ROOT_4LEVEL) {
+		cr3 = root_hpa | kvm_get_active_pcid(vcpu);
+	} else {
+		/* PCID in the guest should be impossible with a 32-bit MMU. */
+		WARN_ON_ONCE(kvm_get_active_pcid(vcpu));
+		cr3 = root_hpa;
 	}
 
 	svm->vmcb->save.cr3 = cr3;