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SubjectRe: [PATCH v2 1/3] KVM: x86: Add EMULTYPE_PF when emulation is triggered by a page fault
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On 2/19/2020 7:03 AM, Sean Christopherson wrote:
> Add a new emulation type flag to explicitly mark emulation related to a
> page fault. Move the propation of the GPA into the emulator from the
> page fault handler into x86_emulate_instruction, using EMULTYPE_PF as an
> indicator that cr2 is valid. Similarly, don't propagate cr2 into the
> exception.address when it's *not* valid.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> arch/x86/include/asm/kvm_host.h | 12 +++++++++---
> arch/x86/kvm/mmu/mmu.c | 10 ++--------
> arch/x86/kvm/x86.c | 25 +++++++++++++++++++------
> 3 files changed, 30 insertions(+), 17 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 4dffbc10d3f8..10c1e8f472b6 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1370,8 +1370,9 @@ extern u64 kvm_mce_cap_supported;
> * decode the instruction length. For use *only* by
> * kvm_x86_ops->skip_emulated_instruction() implementations.
> *
> - * EMULTYPE_ALLOW_RETRY - Set when the emulator should resume the guest to
> - * retry native execution under certain conditions.
> + * EMULTYPE_ALLOW_RETRY_PF - Set when the emulator should resume the guest to
> + * retry native execution under certain conditions,
> + * Can only be set in conjunction with EMULTYPE_PF.
> *
> * EMULTYPE_TRAP_UD_FORCED - Set when emulating an intercepted #UD that was
> * triggered by KVM's magic "force emulation" prefix,
> @@ -1384,13 +1385,18 @@ extern u64 kvm_mce_cap_supported;
> * backdoor emulation, which is opt in via module param.
> * VMware backoor emulation handles select instructions
> * and reinjects the #GP for all other cases.
> + *
> + * EMULTYPE_PF - Set when emulating MMIO by way of an intercepted #PF, in which
> + * case the CR2/GPA value pass on the stack is valid.
> */
> #define EMULTYPE_NO_DECODE (1 << 0)
> #define EMULTYPE_TRAP_UD (1 << 1)
> #define EMULTYPE_SKIP (1 << 2)
> -#define EMULTYPE_ALLOW_RETRY (1 << 3)
> +#define EMULTYPE_ALLOW_RETRY_PF (1 << 3)

How about naming it as EMULTYPE_PF_ALLOW_RETRY and exchanging the bit
position with EMULTYPE_PF ?

> #define EMULTYPE_TRAP_UD_FORCED (1 << 4)
> #define EMULTYPE_VMWARE_GP (1 << 5)
> +#define EMULTYPE_PF (1 << 6)
> +
> int kvm_emulate_instruction(struct kvm_vcpu *vcpu, int emulation_type);
> int kvm_emulate_instruction_from_buffer(struct kvm_vcpu *vcpu,
> void *insn, int insn_len);
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 7011a4e54866..258624d46588 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -5416,18 +5416,12 @@ EXPORT_SYMBOL_GPL(kvm_mmu_unprotect_page_virt);
> int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 error_code,
> void *insn, int insn_len)
> {
> - int r, emulation_type = 0;
> + int r, emulation_type = EMULTYPE_PF;
> bool direct = vcpu->arch.mmu->direct_map;
>
> if (WARN_ON(!VALID_PAGE(vcpu->arch.mmu->root_hpa)))
> return RET_PF_RETRY;
>
> - /* With shadow page tables, fault_address contains a GVA or nGPA. */
> - if (vcpu->arch.mmu->direct_map) {
> - vcpu->arch.gpa_available = true;
> - vcpu->arch.gpa_val = cr2_or_gpa;
> - }
> -
> r = RET_PF_INVALID;
> if (unlikely(error_code & PFERR_RSVD_MASK)) {
> r = handle_mmio_page_fault(vcpu, cr2_or_gpa, direct);
> @@ -5472,7 +5466,7 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 error_code,
> * for L1 isn't going to magically fix whatever issue cause L2 to fail.
> */
> if (!mmio_info_in_cache(vcpu, cr2_or_gpa, direct) && !is_guest_mode(vcpu))
> - emulation_type = EMULTYPE_ALLOW_RETRY;
> + emulation_type |= EMULTYPE_ALLOW_RETRY_PF;
> emulate:
> /*
> * On AMD platforms, under certain conditions insn_len may be zero on #NPF.
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index fbabb2f06273..92af6c5a69e3 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6483,10 +6483,11 @@ static bool reexecute_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> gpa_t gpa = cr2_or_gpa;
> kvm_pfn_t pfn;
>
> - if (!(emulation_type & EMULTYPE_ALLOW_RETRY))
> + if (!(emulation_type & EMULTYPE_ALLOW_RETRY_PF))
> return false;
>
> - if (WARN_ON_ONCE(is_guest_mode(vcpu)))
> + if (WARN_ON_ONCE(is_guest_mode(vcpu)) ||
> + WARN_ON_ONCE(!(emulation_type & EMULTYPE_PF)))
> return false;
>
> if (!vcpu->arch.mmu->direct_map) {
> @@ -6574,10 +6575,11 @@ static bool retry_instruction(struct x86_emulate_ctxt *ctxt,
> */
> vcpu->arch.last_retry_eip = vcpu->arch.last_retry_addr = 0;
>
> - if (!(emulation_type & EMULTYPE_ALLOW_RETRY))
> + if (!(emulation_type & EMULTYPE_ALLOW_RETRY_PF))
> return false;
>
> - if (WARN_ON_ONCE(is_guest_mode(vcpu)))
> + if (WARN_ON_ONCE(is_guest_mode(vcpu)) ||
> + WARN_ON_ONCE(!(emulation_type & EMULTYPE_PF)))
> return false;
>
> if (x86_page_table_writing_insn(ctxt))
> @@ -6830,8 +6832,19 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> }
>
> restart:
> - /* Save the faulting GPA (cr2) in the address field */
> - ctxt->exception.address = cr2_or_gpa;
> + if (emulation_type & EMULTYPE_PF) {
> + /* Save the faulting GPA (cr2) in the address field */
> + ctxt->exception.address = cr2_or_gpa;
> +
> + /* With shadow page tables, cr2 contains a GVA or nGPA. */
> + if (vcpu->arch.mmu->direct_map) {
> + vcpu->arch.gpa_available = true;
> + vcpu->arch.gpa_val = cr2_or_gpa;
> + }
> + } else {
> + /* Sanitize the address out of an abundance of paranoia. */
> + ctxt->exception.address = 0;
> + }
>
> r = x86_emulate_insn(ctxt);
>
>

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