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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 2/21/2020 4:11 AM, Sean Christopherson wrote:
    > On Wed, Feb 19, 2020 at 05:01:41PM +0800, Xiaoyao Li wrote:
    >> 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 ?
    >
    > Hmm, EMULTYPE_PF_ALLOW_RETRY does sound better. I'm on the fence regarding
    > shuffling the bits. If I were to shuffle the bits, I'd do a more thorough
    > reorder so that the #UD and #PF types are consecutive, e.g.
    >
    > #define EMULTYPE_NO_DECODE (1 << 0)
    > #define EMULTYPE_TRAP_UD (1 << 1)
    > #define EMULTYPE_TRAP_UD_FORCED (1 << 2)
    > #define EMULTYPE_SKIP (1 << 3)
    > #define EMULTYPE_VMWARE_GP (1 << 4)
    > #define EMULTYPE_PF (1 << 5)
    > #define EMULTYPE_PF_ALLOW_RETRY (1 << 6)
    >
    > Part of me really wants to do that, the other part of me thinks it's
    > unnecessary thrash.
    >

    I'm fine with thorough reorder, it helps read the codes.
    It's up to Paolo, anyway.

    >>> #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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