Messages in this thread | | | Date | Wed, 31 Aug 2022 11:17:59 +0800 | From | "Hou Wenlong" <> | Subject | Re: [PATCH 1/2] KVM: x86: Return emulator error if RDMSR/WRMSR emulation failed |
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On Wed, Aug 31, 2022 at 02:44:08AM +0800, Sean Christopherson wrote: > On Thu, Jul 28, 2022, Hou Wenlong wrote: > > The return value of emulator_{get|set}_mst_with_filter() > > is confused, since msr access error and emulator error > > are mixed. Although, KVM_MSR_RET_* doesn't conflict with > > X86EMUL_IO_NEEDED at present, it is better to convert > > msr access error to emulator error if error value is > > needed. > > > > Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com> > > --- > > arch/x86/kvm/x86.c | 22 ++++++++++++---------- > > 1 file changed, 12 insertions(+), 10 deletions(-) > > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > index 5366f884e9a7..8df89b9c212f 100644 > > --- a/arch/x86/kvm/x86.c > > +++ b/arch/x86/kvm/x86.c > > @@ -7908,11 +7908,12 @@ static int emulator_get_msr_with_filter(struct x86_emulate_ctxt *ctxt, > > int r; > > > > r = kvm_get_msr_with_filter(vcpu, msr_index, pdata); > > - > > - if (r && kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_RDMSR, 0, > > - complete_emulated_rdmsr, r)) { > > - /* Bounce to user space */ > > - return X86EMUL_IO_NEEDED; > > + if (r) { > > + if (kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_RDMSR, 0, > > + complete_emulated_rdmsr, r)) > > + r = X86EMUL_IO_NEEDED; > > + else > > + r = X86EMUL_UNHANDLEABLE; > > This should be X86EMUL_PROPAGATE_FAULT, X86EMUL_UNHANDLEABLE is used to indicate > that KVM needs to bail all the way to userspace. > > I definitely like the idea of converting to X86EMUL_* here instead of spreading > it across these helpers and the emulator, but in that case should convert _all_ > types. > > And I think it makes sense to opportunistically handle "r < 0" in the get helper. > KVM may not return -errno today, but assuming that will always hold true is > unnecessarily risking. I agree. The original commit 7dffecaf4eab wanted to report negative values to userspace, but the emulator actually didn't propagate -errno to the caller. So handling "r < 0" in the set helper is better, then only X86EMUL_* is returned.
> > E.g. what about: > > > static int emulator_get_msr_with_filter(struct x86_emulate_ctxt *ctxt, > u32 msr_index, u64 *pdata) > { > struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt); > int r; > > r = kvm_get_msr_with_filter(vcpu, msr_index, pdata); > if (r < 0) > return X86EMUL_UNHANDLEABLE; > > if (r) { > if (kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_RDMSR, 0, > complete_emulated_rdmsr, r)) > return X86EMUL_IO_NEEDED; > else > return X86EMUL_PROPAGATE_FAULT; > } > > return X86EMUL_CONTINUE; > } > > static int emulator_set_msr_with_filter(struct x86_emulate_ctxt *ctxt, > u32 msr_index, u64 data) > { > struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt); > int r; > > r = kvm_set_msr_with_filter(vcpu, msr_index, data); > if (r < 0) > return X86EMUL_UNHANDLEABLE; > > if (r) { > if (kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_WRMSR, data, > complete_emulated_msr_access, r)) > return X86EMUL_IO_NEEDED; > else > return X86EMUL_PROPAGATE_FAULT; > } > > return X86EMUL_CONTINUE; > } > I'll take this in the v2. Thanks.
> > Or maybe even add a helper to do the translation? Can't tell if this is a net > positive or not. It's a bit gratuitous, but it does ensure consistent behavior > for RDMSR vs. WRMSR. > > static int emulator_handle_msr_return(struct kvm_vcpu *vcpu *, int r, > u32 msr, u64 data, u32 exit_reason, > int (*comp)(struct kvm_vcpu *vcpu)) > { > if (r < 0) > return X86EMUL_UNHANDLEABLE; > > if (r) { > if (kvm_msr_user_space(vcpu, msr, exit_reason, data, comp, r)) > return X86EMUL_IO_NEEDED; > else > return X86EMUL_UNHANDLEABLE; > } > > return X86EMUL_CONTINUE; > } > > static int emulator_get_msr_with_filter(struct x86_emulate_ctxt *ctxt, > u32 msr_index, u64 *pdata) > { > struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt); > int r; > > r = kvm_get_msr_with_filter(vcpu, msr_index, pdata); > return emulator_handle_msr_return(vcpu, r, msr_index, 0, > KVM_EXIT_X86_RDMSR, > complete_emulated_rdmsr); > } > > static int emulator_set_msr_with_filter(struct x86_emulate_ctxt *ctxt, > u32 msr_index, u64 data) > { > struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt); > int r; > > r = kvm_set_msr_with_filter(vcpu, msr_index, data); > return emulator_handle_msr_return(vcpu, r, msr_index, data, > KVM_EXIT_X86_WRMSR, > complete_emulated_msr_access); > } > > > And then the emulator side of things can be: > > static int em_wrmsr(struct x86_emulate_ctxt *ctxt) > { > u64 msr_index = reg_read(ctxt, VCPU_REGS_RCX); > u64 msr_data; > int r; > > msr_data = (u32)reg_read(ctxt, VCPU_REGS_RAX) > | ((u64)reg_read(ctxt, VCPU_REGS_RDX) << 32); > r = ctxt->ops->set_msr_with_filter(ctxt, msr_index, msr_data); > > if (r == X86EMUL_PROPAGATE_FAULT) > return emulate_gp(ctxt, 0); > > return r; > } > > static int em_rdmsr(struct x86_emulate_ctxt *ctxt) > { > u64 msr_index = reg_read(ctxt, VCPU_REGS_RCX); > u64 msr_data; > int r; > > r = ctxt->ops->get_msr_with_filter(ctxt, msr_index, &msr_data); > > if (r == X86EMUL_PROPAGATE_FAULT) > return emulate_gp(ctxt, 0); > > if (r == X86EMUL_CONTINUE) { > *reg_write(ctxt, VCPU_REGS_RAX) = (u32)msr_data; > *reg_write(ctxt, VCPU_REGS_RDX) = msr_data >> 32; > } > return r; > }
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