Re: [PATCH v4 3/5] KVM: x86: clean up reexecute_instruction

Marcelo Tosatti
2013-01-04T22:21:35Z

On Fri, Jan 04, 2013 at 09:55:40PM +0800, Xiao Guangrong wrote:
> Little cleanup for reexecute_instruction, also use gpa_to_gfn in
> retry_instruction
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
> ---
> arch/x86/kvm/x86.c | 13 ++++++-------
> 1 files changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 1c9c834..ad39018 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4761,19 +4761,18 @@ static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t gva)
> if (tdp_enabled)
> return false;
>
> + gpa = kvm_mmu_gva_to_gpa_read(vcpu, gva, NULL);
> + if (gpa == UNMAPPED_GVA)
> + return true; /* let cpu generate fault */
> +

Why change from _system to _read here? Purely cleanup patch should
have no logical changes.

BTW, there is not much logic in using reexecute_instruction() at
for x86_decode_insn (checks in reexecute_instruction() assume
write to the cr2, for instance).
Fault propagation for x86_decode_insn seems completly broken
(which is perhaps why reexecute_instruction() there survived).

> /*
> * if emulation was due to access to shadowed page table
> * and it failed try to unshadow page and re-enter the
> * guest to let CPU execute the instruction.
> */
> - if (kvm_mmu_unprotect_page_virt(vcpu, gva))
> + if (kvm_mmu_unprotect_page(vcpu->kvm, gpa_to_gfn(gpa)))
> return true;
>
> - gpa = kvm_mmu_gva_to_gpa_system(vcpu, gva, NULL);
> -
> - if (gpa == UNMAPPED_GVA)
> - return true; /* let cpu generate fault */
> -
> /*
> * Do not retry the unhandleable instruction if it faults on the
> * readonly host memory, otherwise it will goto a infinite loop:
> @@ -4828,7 +4827,7 @@ static bool retry_instruction(struct x86_emulate_ctxt *ctxt,
> if (!vcpu->arch.mmu.direct_map)
> gpa = kvm_mmu_gva_to_gpa_write(vcpu, cr2, NULL);
>
> - kvm_mmu_unprotect_page(vcpu->kvm, gpa >> PAGE_SHIFT);
> + kvm_mmu_unprotect_page(vcpu->kvm, gpa_to_gfn(gpa));
>
> return true;
> }
> --
> 1.7.7.6