KVM: x86/mmu: Handle MMIO SPTEs directly in mmu_set_spte()

Now that it should be impossible to convert a valid SPTE to an MMIO SPTE,
handle MMIO SPTEs early in mmu_set_spte() without going through
set_spte() and all the logic for removing an existing, valid SPTE.
The other caller of set_spte(), FNAME(sync_page)(), explicitly handles
MMIO SPTEs prior to calling set_spte().

This simplifies mmu_set_spte() and set_spte(), and also "fixes" an oddity
where MMIO SPTEs are traced by both trace_kvm_mmu_set_spte() and
trace_mark_mmio_spte().

Note, mmu_spte_set() will WARN if this new approach causes KVM to create
an MMIO SPTE overtop a valid SPTE.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210225204749.1512652-8-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index dd946fb0b5bc326dcc5de3630d57c40df9af4022..51935510bad96ff9943e044dd100296050ab0b8e 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -236,17 +236,6 @@ static unsigned get_mmio_spte_access(u64 spte)
        return spte & shadow_mmio_access_mask;
 }
 
-static bool set_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, gfn_t gfn,
-                         kvm_pfn_t pfn, unsigned int access)
-{
-       if (unlikely(is_noslot_pfn(pfn))) {
-               mark_mmio_spte(vcpu, sptep, gfn, access);
-               return true;
-       }
-
-       return false;
-}
-
 static bool check_mmio_spte(struct kvm_vcpu *vcpu, u64 spte)
 {
        u64 kvm_gen, spte_gen, gen;
@@ -2563,9 +2552,6 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
        struct kvm_mmu_page *sp;
        int ret;
 
-       if (set_mmio_spte(vcpu, sptep, gfn, pfn, pte_access))
-               return 0;
-
        sp = sptep_to_sp(sptep);
 
        ret = make_spte(vcpu, pte_access, level, gfn, pfn, *sptep, speculative,
@@ -2595,6 +2581,11 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
        pgprintk("%s: spte %llx write_fault %d gfn %llx\n", __func__,
                 *sptep, write_fault, gfn);
 
+       if (unlikely(is_noslot_pfn(pfn))) {
+               mark_mmio_spte(vcpu, sptep, gfn, pte_access);
+               return RET_PF_EMULATE;
+       }
+
        if (is_shadow_present_pte(*sptep)) {
                /*
                 * If we overwrite a PTE page pointer with a 2MB PMD, unlink
@@ -2628,9 +2619,6 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
                kvm_flush_remote_tlbs_with_address(vcpu->kvm, gfn,
                                KVM_PAGES_PER_HPAGE(level));
 
-       if (unlikely(is_mmio_spte(*sptep)))
-               ret = RET_PF_EMULATE;
-
        /*
         * The fault is fully spurious if and only if the new SPTE and old SPTE
         * are identical, and emulation is not required.