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Date: Thu, 20 Feb 2020 12:11:45 -0800
From: Sean Christopherson <sean.j.christopherson@...el.com>
To: Xiaoyao Li <xiaoyao.li@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] KVM: x86: Add EMULTYPE_PF when emulation is
triggered by a page fault
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@...el.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.
> > #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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