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    Subject[PATCH RFC v7 49/64] KVM: SVM: Introduce ops for the post gfn map and unmap
    Date
    From: Brijesh Singh <brijesh.singh@amd.com>

    When SEV-SNP is enabled in the guest VM, the guest memory pages can
    either be a private or shared. A write from the hypervisor goes through
    the RMP checks. If the CPU sees that hypervisor is attempting to write
    to a guest private page, then it will trigger an RMP violation #PF.

    To avoid the RMP violation with GHCB pages, added new
    post_{map,unmap}_gfn functions to verify if its safe to map GHCB pages.
    Use kvm->mmu_lock to guard the GHCB against invalidations while being
    accessed.

    Need to add generic post_{map,unmap}_gfn() ops that can be used to
    verify that it's safe to map a given guest page in the hypervisor.

    Link: https://lore.kernel.org/all/CABpDEukAEGwb9w12enO=fhSbHbchypsOdO2dkR4Jei3wDW6NWg@mail.gmail.com/
    Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
    Signed-off-by: Jarkko Sakkinen <jarkko@profian.com>
    Signed-off by: Ashish Kalra <ashish.kalra@amd.com>
    [mdr: use kvm->mmu_lock instead of a new spinlock, this should guard
    GHCB page against invalidations]
    Signed-off-by: Michael Roth <michael.roth@amd.com>
    ---
    arch/x86/kvm/svm/sev.c | 40 ++++++++++++++++++++++++++++++++++++++--
    arch/x86/kvm/svm/svm.h | 3 +++
    2 files changed, 41 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
    index abe6444bf5d4..90b509fe1826 100644
    --- a/arch/x86/kvm/svm/sev.c
    +++ b/arch/x86/kvm/svm/sev.c
    @@ -2926,19 +2926,28 @@ static inline int svm_map_ghcb(struct vcpu_svm *svm, struct kvm_host_map *map)
    {
    struct vmcb_control_area *control = &svm->vmcb->control;
    u64 gfn = gpa_to_gfn(control->ghcb_gpa);
    + struct kvm_vcpu *vcpu = &svm->vcpu;

    - if (kvm_vcpu_map(&svm->vcpu, gfn, map)) {
    + if (kvm_vcpu_map(vcpu, gfn, map)) {
    /* Unable to map GHCB from guest */
    pr_err("error mapping GHCB GFN [%#llx] from guest\n", gfn);
    return -EFAULT;
    }

    + if (sev_post_map_gfn(vcpu->kvm, map->gfn, map->pfn)) {
    + kvm_vcpu_unmap(vcpu, map, false);
    + return -EBUSY;
    + }
    +
    return 0;
    }

    static inline void svm_unmap_ghcb(struct vcpu_svm *svm, struct kvm_host_map *map)
    {
    - kvm_vcpu_unmap(&svm->vcpu, map, true);
    + struct kvm_vcpu *vcpu = &svm->vcpu;
    +
    + kvm_vcpu_unmap(vcpu, map, true);
    + sev_post_unmap_gfn(vcpu->kvm, map->gfn, map->pfn);
    }

    static void dump_ghcb(struct vcpu_svm *svm)
    @@ -3875,6 +3884,33 @@ void sev_rmp_page_level_adjust(struct kvm *kvm, gfn_t gfn, int *level)
    __func__, gfn, *level, rmp_level, ret);
    }

    +int sev_post_map_gfn(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn)
    +{
    + int level;
    +
    + if (!sev_snp_guest(kvm))
    + return 0;
    +
    + read_lock(&(kvm)->mmu_lock);
    +
    + /* If pfn is not added as private then fail */
    + if (snp_lookup_rmpentry(pfn, &level) == 1) {
    + read_unlock(&(kvm)->mmu_lock);
    + pr_err_ratelimited("failed to map private gfn 0x%llx pfn 0x%llx\n", gfn, pfn);
    + return -EBUSY;
    + }
    +
    + return 0;
    +}
    +
    +void sev_post_unmap_gfn(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn)
    +{
    + if (!sev_snp_guest(kvm))
    + return;
    +
    + read_unlock(&(kvm)->mmu_lock);
    +}
    +
    int sev_fault_is_private(struct kvm *kvm, gpa_t gpa, u64 error_code, bool *private_fault)
    {
    gfn_t gfn = gpa_to_gfn(gpa);
    diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
    index a4d48c3e0f89..aef13c120f2d 100644
    --- a/arch/x86/kvm/svm/svm.h
    +++ b/arch/x86/kvm/svm/svm.h
    @@ -100,6 +100,7 @@ struct kvm_sev_info {
    atomic_t migration_in_progress;
    u64 snp_init_flags;
    void *snp_context; /* SNP guest context page */
    + spinlock_t psc_lock;
    };

    struct kvm_svm {
    @@ -727,6 +728,8 @@ void sev_es_prepare_switch_to_guest(struct sev_es_save_area *hostsa);
    void sev_es_unmap_ghcb(struct vcpu_svm *svm);
    struct page *snp_safe_alloc_page(struct kvm_vcpu *vcpu);
    void sev_rmp_page_level_adjust(struct kvm *kvm, gfn_t gfn, int *level);
    +int sev_post_map_gfn(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn);
    +void sev_post_unmap_gfn(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn);

    int sev_fault_is_private(struct kvm *kvm, gpa_t gpa, u64 error_code, bool *private_fault);

    --
    2.25.1
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