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Date: Fri, 21 Feb 2020 10:59:21 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Sean Christopherson <sean.j.christopherson@...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 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@...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.
>
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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