On Tue, Sep 02, 2014 at 05:13:49PM +0200, Paolo Bonzini wrote:
> This is required for the following patch to work correctly. If a nested page
> fault happens during emulation, we must inject a vmexit, not a page fault.
> Luckily we already have the required machinery: it is enough to return
> X86EMUL_INTERCEPTED instead of X86EMUL_PROPAGATE_FAULT.
>
I wonder why this patch is needed. X86EMUL_PROPAGATE_FAULT causes
ctxt->have_exception to be set to true in x86_emulate_insn().
x86_emulate_instruction() checks ctxt->have_exception and calls
inject_emulated_exception() if it is true. inject_emulated_exception()
calls kvm_propagate_fault() where we check if the fault was nested and
generate vmexit or a page fault accordingly.
> Reported-by: Valentine Sinitsyn <valentine.sinitsyn@xxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 18 ++++++++++++++----
> 1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e4ed85e07a01..9e3b74c044ed 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -416,6 +416,16 @@ void kvm_propagate_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault)
> vcpu->arch.mmu.inject_page_fault(vcpu, fault);
> }
>
> +static inline int kvm_propagate_or_intercept(struct kvm_vcpu *vcpu,
> + struct x86_exception *exception)
> +{
> + if (likely(!exception->nested_page_fault))
> + return X86EMUL_PROPAGATE_FAULT;
> +
> + vcpu->arch.mmu.inject_page_fault(vcpu, exception);
> + return X86EMUL_INTERCEPTED;
> +}
> +
> void kvm_inject_nmi(struct kvm_vcpu *vcpu)
> {
> atomic_inc(&vcpu->arch.nmi_queued);
> @@ -4122,7 +4132,7 @@ static int kvm_read_guest_virt_helper(gva_t addr, void *val, unsigned int bytes,
> int ret;
>
> if (gpa == UNMAPPED_GVA)
> - return X86EMUL_PROPAGATE_FAULT;
> + return kvm_propagate_or_intercept(vcpu, exception);
> ret = kvm_read_guest_page(vcpu->kvm, gpa >> PAGE_SHIFT, data,
> offset, toread);
> if (ret < 0) {
> @@ -4152,7 +4162,7 @@ static int kvm_fetch_guest_virt(struct x86_emulate_ctxt *ctxt,
> gpa_t gpa = vcpu->arch.walk_mmu->gva_to_gpa(vcpu, addr, access|PFERR_FETCH_MASK,
> exception);
> if (unlikely(gpa == UNMAPPED_GVA))
> - return X86EMUL_PROPAGATE_FAULT;
> + return kvm_propagate_or_intercept(vcpu, exception);
>
> offset = addr & (PAGE_SIZE-1);
> if (WARN_ON(offset + bytes > PAGE_SIZE))
> @@ -4203,7 +4213,7 @@ int kvm_write_guest_virt_system(struct x86_emulate_ctxt *ctxt,
> int ret;
>
> if (gpa == UNMAPPED_GVA)
> - return X86EMUL_PROPAGATE_FAULT;
> + return kvm_propagate_or_intercept(vcpu, exception);
> ret = kvm_write_guest(vcpu->kvm, gpa, data, towrite);
> if (ret < 0) {
> r = X86EMUL_IO_NEEDED;
> @@ -4350,7 +4360,7 @@ static int emulator_read_write_onepage(unsigned long addr, void *val,
> ret = vcpu_mmio_gva_to_gpa(vcpu, addr, &gpa, exception, write);
>
> if (ret < 0)
> - return X86EMUL_PROPAGATE_FAULT;
> + return kvm_propagate_or_intercept(vcpu, exception);
>
> /* For APIC access vmexit */
> if (ret)
> --
> 1.8.3.1
>
>
--
Gleb.
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