On Mon, Sep 21, 2020 at 04:19:21PM +0300, Maxim Levitsky wrote:
> This will allow us to make some MSR writes fatal to the guest
> (e.g when out of memory condition occurs)
>
> Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> ---
> arch/x86/kvm/emulate.c | 7 +++++--
> arch/x86/kvm/x86.c | 5 +++--
> 2 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 1d450d7710d63..d855304f5a509 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -3702,13 +3702,16 @@ static int em_dr_write(struct x86_emulate_ctxt *ctxt)
> static int em_wrmsr(struct x86_emulate_ctxt *ctxt)
> {
> u64 msr_data;
> + int ret;
>
> msr_data = (u32)reg_read(ctxt, VCPU_REGS_RAX)
> | ((u64)reg_read(ctxt, VCPU_REGS_RDX) << 32);
> - if (ctxt->ops->set_msr(ctxt, reg_read(ctxt, VCPU_REGS_RCX), msr_data))
> +
> + ret = ctxt->ops->set_msr(ctxt, reg_read(ctxt, VCPU_REGS_RCX), msr_data);
> + if (ret > 0)
> return emulate_gp(ctxt, 0);
>
> - return X86EMUL_CONTINUE;
> + return ret < 0 ? X86EMUL_UNHANDLEABLE : X86EMUL_CONTINUE;
> }
>
> static int em_rdmsr(struct x86_emulate_ctxt *ctxt)
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 063d70e736f7f..b6c67ab7c4f34 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1612,15 +1612,16 @@ int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu)
> {
> u32 ecx = kvm_rcx_read(vcpu);
> u64 data = kvm_read_edx_eax(vcpu);
> + int ret = kvm_set_msr(vcpu, ecx, data);
>
> - if (kvm_set_msr(vcpu, ecx, data)) {
> + if (ret > 0) {
> trace_kvm_msr_write_ex(ecx, data);
> kvm_inject_gp(vcpu, 0);
> return 1;
> }
>
> trace_kvm_msr_write(ecx, data);
Tracing the access as non-faulting feels wrong. The WRMSR has not completed,
e.g. if userspace cleanly handles -ENOMEM and restarts the guest, KVM would
trace the WRMSR twice.
What about:
int ret = kvm_set_msr(vcpu, ecx, data);
if (ret < 0)
return ret;
if (ret) {
trace_kvm_msr_write_ex(ecx, data);
kvm_inject_gp(vcpu, 0);
return 1;
}
trace_kvm_msr_write(ecx, data);
return kvm_skip_emulated_instruction(vcpu);
> - return kvm_skip_emulated_instruction(vcpu);
> + return ret < 0 ? ret : kvm_skip_emulated_instruction(vcpu);
> }
> EXPORT_SYMBOL_GPL(kvm_emulate_wrmsr);
>
> --
> 2.26.2
>
