| Message ID | 20200731214947.16885-2-graf@amazon.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Allow user space to restrict and augment MSR emulation | expand |
On Fri, Jul 31, 2020 at 2:50 PM Alexander Graf <graf@amazon.com> wrote: > > MSRs are weird. Some of them are normal control registers, such as EFER. > Some however are registers that really are model specific, not very > interesting to virtualization workloads, and not performance critical. > Others again are really just windows into package configuration. > > Out of these MSRs, only the first category is necessary to implement in > kernel space. Rarely accessed MSRs, MSRs that should be fine tunes against > certain CPU models and MSRs that contain information on the package level > are much better suited for user space to process. However, over time we have > accumulated a lot of MSRs that are not the first category, but still handled > by in-kernel KVM code. > > This patch adds a generic interface to handle WRMSR and RDMSR from user > space. With this, any future MSR that is part of the latter categories can > be handled in user space. > > Furthermore, it allows us to replace the existing "ignore_msrs" logic with > something that applies per-VM rather than on the full system. That way you > can run productive VMs in parallel to experimental ones where you don't care > about proper MSR handling. > > Signed-off-by: Alexander Graf <graf@amazon.com> > > --- > > v1 -> v2: > > - s/ETRAP_TO_USER_SPACE/ENOENT/g > - deflect all #GP injection events to user space, not just unknown MSRs. > That was we can also deflect allowlist errors later > - fix emulator case > > v2 -> v3: > > - return r if r == X86EMUL_IO_NEEDED > - s/KVM_EXIT_RDMSR/KVM_EXIT_X86_RDMSR/g > - s/KVM_EXIT_WRMSR/KVM_EXIT_X86_WRMSR/g > - Use complete_userspace_io logic instead of reply field > - Simplify trapping code > --- > Documentation/virt/kvm/api.rst | 62 +++++++++++++++++++ > arch/x86/include/asm/kvm_host.h | 6 ++ > arch/x86/kvm/emulate.c | 18 +++++- > arch/x86/kvm/x86.c | 106 ++++++++++++++++++++++++++++++-- > include/trace/events/kvm.h | 2 +- > include/uapi/linux/kvm.h | 10 +++ > 6 files changed, 197 insertions(+), 7 deletions(-) > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > index 320788f81a05..79c3e2fdfae4 100644 > --- a/Documentation/virt/kvm/api.rst > +++ b/Documentation/virt/kvm/api.rst The new exit reasons should probably be mentioned here (around line 4866): .. note:: For KVM_EXIT_IO, KVM_EXIT_MMIO, KVM_EXIT_OSI, KVM_EXIT_PAPR and KVM_EXIT_EPR the corresponding operations are complete (and guest state is consistent) only after userspace has re-entered the kernel with KVM_RUN. The kernel side will first finish incomplete operations and then check for pending signals. Userspace can re-enter the guest with an unmasked signal pending to complete pending operations. Other than that, my remaining comments are all nits. Feel free to ignore them. > +static int kvm_get_msr_user_space(struct kvm_vcpu *vcpu, u32 index) Return bool rather than int? > +{ > + if (!vcpu->kvm->arch.user_space_msr_enabled) > + return 0; > + > + vcpu->run->exit_reason = KVM_EXIT_X86_RDMSR; > + vcpu->run->msr.error = 0; Should we clear 'pad' in case anyone can think of a reason to use this space to extend the API in the future? > + vcpu->run->msr.index = index; > + vcpu->arch.pending_user_msr = true; > + vcpu->arch.complete_userspace_io = complete_emulated_rdmsr; complete_userspace_io could perhaps be renamed to complete_userspace_emulation (in a separate commit). > + > + return 1; > +} > + > +static int kvm_set_msr_user_space(struct kvm_vcpu *vcpu, u32 index, u64 data) Return bool rather than int? > +{ > + if (!vcpu->kvm->arch.user_space_msr_enabled) > + return 0; > + > + vcpu->run->exit_reason = KVM_EXIT_X86_WRMSR; > + vcpu->run->msr.error = 0; Same question about 'pad' as above. > + vcpu->run->msr.index = index; > + vcpu->run->msr.data = data; > + vcpu->arch.pending_user_msr = true; > + vcpu->arch.complete_userspace_io = complete_emulated_wrmsr; > + > + return 1; > +} > + Reviewed-by: Jim Mattson <jmattson@google.com>
On 01.08.20 01:36, Jim Mattson wrote: > > On Fri, Jul 31, 2020 at 2:50 PM Alexander Graf <graf@amazon.com> wrote: >> >> MSRs are weird. Some of them are normal control registers, such as EFER. >> Some however are registers that really are model specific, not very >> interesting to virtualization workloads, and not performance critical. >> Others again are really just windows into package configuration. >> >> Out of these MSRs, only the first category is necessary to implement in >> kernel space. Rarely accessed MSRs, MSRs that should be fine tunes against >> certain CPU models and MSRs that contain information on the package level >> are much better suited for user space to process. However, over time we have >> accumulated a lot of MSRs that are not the first category, but still handled >> by in-kernel KVM code. >> >> This patch adds a generic interface to handle WRMSR and RDMSR from user >> space. With this, any future MSR that is part of the latter categories can >> be handled in user space. >> >> Furthermore, it allows us to replace the existing "ignore_msrs" logic with >> something that applies per-VM rather than on the full system. That way you >> can run productive VMs in parallel to experimental ones where you don't care >> about proper MSR handling. >> >> Signed-off-by: Alexander Graf <graf@amazon.com> >> >> --- >> >> v1 -> v2: >> >> - s/ETRAP_TO_USER_SPACE/ENOENT/g >> - deflect all #GP injection events to user space, not just unknown MSRs. >> That was we can also deflect allowlist errors later >> - fix emulator case >> >> v2 -> v3: >> >> - return r if r == X86EMUL_IO_NEEDED >> - s/KVM_EXIT_RDMSR/KVM_EXIT_X86_RDMSR/g >> - s/KVM_EXIT_WRMSR/KVM_EXIT_X86_WRMSR/g >> - Use complete_userspace_io logic instead of reply field >> - Simplify trapping code >> --- >> Documentation/virt/kvm/api.rst | 62 +++++++++++++++++++ >> arch/x86/include/asm/kvm_host.h | 6 ++ >> arch/x86/kvm/emulate.c | 18 +++++- >> arch/x86/kvm/x86.c | 106 ++++++++++++++++++++++++++++++-- >> include/trace/events/kvm.h | 2 +- >> include/uapi/linux/kvm.h | 10 +++ >> 6 files changed, 197 insertions(+), 7 deletions(-) >> >> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst >> index 320788f81a05..79c3e2fdfae4 100644 >> --- a/Documentation/virt/kvm/api.rst >> +++ b/Documentation/virt/kvm/api.rst > > The new exit reasons should probably be mentioned here (around line 4866): > > .. note:: > > For KVM_EXIT_IO, KVM_EXIT_MMIO, KVM_EXIT_OSI, KVM_EXIT_PAPR and > KVM_EXIT_EPR the corresponding > > operations are complete (and guest state is consistent) only after userspace > has re-entered the kernel with KVM_RUN. The kernel side will first finish > incomplete operations and then check for pending signals. Userspace > can re-enter the guest with an unmasked signal pending to complete > pending operations. Great catch, thanks! Updated to also include the two new exit reasons. > > Other than that, my remaining comments are all nits. Feel free to ignore them. > >> +static int kvm_get_msr_user_space(struct kvm_vcpu *vcpu, u32 index) > > Return bool rather than int? I'm not a big fan of bool returning APIs unless they have an "is" in their name. In this case, the most readable path forward would probably be an enum: enum kvm_msr_user_space_retval { KVM_MSR_IN_KERNEL, KVM_MSR_BOUNCE_TO_USER_SPACE, }; and then use that in the checks. But that adds a lot of boiler plate for a fully internal, only a few dozen LOC big API. I don't think it's worth it. > >> +{ >> + if (!vcpu->kvm->arch.user_space_msr_enabled) >> + return 0; >> + >> + vcpu->run->exit_reason = KVM_EXIT_X86_RDMSR; >> + vcpu->run->msr.error = 0; > > Should we clear 'pad' in case anyone can think of a reason to use this > space to extend the API in the future? It can't hurt I guess. > >> + vcpu->run->msr.index = index; >> + vcpu->arch.pending_user_msr = true; >> + vcpu->arch.complete_userspace_io = complete_emulated_rdmsr; > > complete_userspace_io could perhaps be renamed to > complete_userspace_emulation (in a separate commit). I think the complicated part of complete_userspace_io is to know it exists and understand how it works. Once you grasp these two bits, the name is just an artifact and IMHO easy enough to apply "beyond I/O". > >> + >> + return 1; >> +} >> + >> +static int kvm_set_msr_user_space(struct kvm_vcpu *vcpu, u32 index, u64 data) > > Return bool rather than int? Same replies as above :). I did get fed up with the amount of duplication though and created a generalized function in v4 that gets called by kvm_get/set_msr_user_space() to ensure that all fields are always set. > >> +{ >> + if (!vcpu->kvm->arch.user_space_msr_enabled) >> + return 0; >> + >> + vcpu->run->exit_reason = KVM_EXIT_X86_WRMSR; >> + vcpu->run->msr.error = 0; > > Same question about 'pad' as above. > >> + vcpu->run->msr.index = index; >> + vcpu->run->msr.data = data; >> + vcpu->arch.pending_user_msr = true; >> + vcpu->arch.complete_userspace_io = complete_emulated_wrmsr; >> + >> + return 1; >> +} >> + > > Reviewed-by: Jim Mattson <jmattson@google.com> Thanks a bunch for the review :) Alex Amazon Development Center Germany GmbH Krausenstr. 38 10117 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B Sitz: Berlin Ust-ID: DE 289 237 879
Alexander Graf <graf@amazon.com> writes: > MSRs are weird. Some of them are normal control registers, such as EFER. > Some however are registers that really are model specific, not very > interesting to virtualization workloads, and not performance critical. > Others again are really just windows into package configuration. > > Out of these MSRs, only the first category is necessary to implement in > kernel space. Rarely accessed MSRs, MSRs that should be fine tunes against > certain CPU models and MSRs that contain information on the package level > are much better suited for user space to process. However, over time we have > accumulated a lot of MSRs that are not the first category, but still handled > by in-kernel KVM code. > > This patch adds a generic interface to handle WRMSR and RDMSR from user > space. With this, any future MSR that is part of the latter categories can > be handled in user space. > > Furthermore, it allows us to replace the existing "ignore_msrs" logic with > something that applies per-VM rather than on the full system. That way you > can run productive VMs in parallel to experimental ones where you don't care > about proper MSR handling. > > Signed-off-by: Alexander Graf <graf@amazon.com> > > --- > > v1 -> v2: > > - s/ETRAP_TO_USER_SPACE/ENOENT/g > - deflect all #GP injection events to user space, not just unknown MSRs. > That was we can also deflect allowlist errors later > - fix emulator case > > v2 -> v3: > > - return r if r == X86EMUL_IO_NEEDED > - s/KVM_EXIT_RDMSR/KVM_EXIT_X86_RDMSR/g > - s/KVM_EXIT_WRMSR/KVM_EXIT_X86_WRMSR/g > - Use complete_userspace_io logic instead of reply field > - Simplify trapping code > --- > Documentation/virt/kvm/api.rst | 62 +++++++++++++++++++ > arch/x86/include/asm/kvm_host.h | 6 ++ > arch/x86/kvm/emulate.c | 18 +++++- > arch/x86/kvm/x86.c | 106 ++++++++++++++++++++++++++++++-- > include/trace/events/kvm.h | 2 +- > include/uapi/linux/kvm.h | 10 +++ > 6 files changed, 197 insertions(+), 7 deletions(-) > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > index 320788f81a05..79c3e2fdfae4 100644 > --- a/Documentation/virt/kvm/api.rst > +++ b/Documentation/virt/kvm/api.rst > @@ -5155,6 +5155,35 @@ Note that KVM does not skip the faulting instruction as it does for > KVM_EXIT_MMIO, but userspace has to emulate any change to the processing state > if it decides to decode and emulate the instruction. > > +:: > + > + /* KVM_EXIT_X86_RDMSR / KVM_EXIT_X86_WRMSR */ > + struct { > + __u8 error; > + __u8 pad[3]; > + __u32 index; > + __u64 data; > + } msr; > + > +Used on x86 systems. When the VM capability KVM_CAP_X86_USER_SPACE_MSR is > +enabled, MSR accesses to registers that would invoke a #GP by KVM kernel code > +will instead trigger a KVM_EXIT_X86_RDMSR exit for reads and KVM_EXIT_X86_WRMSR > +exit for writes. > + > +For KVM_EXIT_X86_RDMSR, the "index" field tells user space which MSR the guest > +wants to read. To respond to this request with a successful read, user space > +writes the respective data into the "data" field and must continue guest > +execution to ensure the read data is transferred into guest register state. > + > +If the RDMSR request was unsuccessful, user space indicates that with a "1" in > +the "error" field. This will inject a #GP into the guest when the VCPU is > +executed again. > + > +For KVM_EXIT_X86_WRMSR, the "index" field tells user space which MSR the guest > +wants to write. Once finished processing the event, user space must continue > +vCPU execution. If the MSR write was unsuccessful, user space also sets the > +"error" field to "1". > + > :: > > /* Fix the size of the union. */ > @@ -5844,6 +5873,28 @@ controlled by the kvm module parameter halt_poll_ns. This capability allows > the maximum halt time to specified on a per-VM basis, effectively overriding > the module parameter for the target VM. > > +7.21 KVM_CAP_X86_USER_SPACE_MSR > +------------------------------- > + > +:Architectures: x86 > +:Target: VM > +:Parameters: args[0] is 1 if user space MSR handling is enabled, 0 otherwise > +:Returns: 0 on success; -1 on error > + > +This capability enables trapping of #GP invoking RDMSR and WRMSR instructions > +into user space. > + > +When a guest requests to read or write an MSR, KVM may not implement all MSRs > +that are relevant to a respective system. It also does not differentiate by > +CPU type. > + > +To allow more fine grained control over MSR handling, user space may enable > +this capability. With it enabled, MSR accesses that would usually trigger > +a #GP event inside the guest by KVM will instead trigger KVM_EXIT_X86_RDMSR > +and KVM_EXIT_X86_WRMSR exit notifications which user space can then handle to > +implement model specific MSR handling and/or user notifications to inform > +a user that an MSR was not handled. > + > 8. Other capabilities. > ====================== > > @@ -6151,3 +6202,14 @@ KVM can therefore start protected VMs. > This capability governs the KVM_S390_PV_COMMAND ioctl and the > KVM_MP_STATE_LOAD MP_STATE. KVM_SET_MP_STATE can fail for protected > guests when the state change is invalid. > + > +8.24 KVM_CAP_X86_USER_SPACE_MSR > +---------------------------- > + > +:Architectures: x86 > + > +This capability indicates that KVM supports deflection of MSR reads and > +writes to user space. It can be enabled on a VM level. If enabled, MSR > +accesses that would usually trigger a #GP by KVM into the guest will > +instead get bounced to user space through the KVM_EXIT_X86_RDMSR and > +KVM_EXIT_X86_WRMSR exit notifications. > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index be5363b21540..809eed0dbdea 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -829,6 +829,9 @@ struct kvm_vcpu_arch { > > /* AMD MSRC001_0015 Hardware Configuration */ > u64 msr_hwcr; > + > + /* User space is handling an MSR request */ > + bool pending_user_msr; > }; > > struct kvm_lpage_info { > @@ -1002,6 +1005,9 @@ struct kvm_arch { > bool guest_can_read_msr_platform_info; > bool exception_payload_enabled; > > + /* Deflect RDMSR and WRMSR to user space when they trigger a #GP */ > + bool user_space_msr_enabled; > + > struct kvm_pmu_event_filter *pmu_event_filter; > struct task_struct *nx_lpage_recovery_thread; > }; > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c > index d0e2825ae617..744ab9c92b73 100644 > --- a/arch/x86/kvm/emulate.c > +++ b/arch/x86/kvm/emulate.c > @@ -3689,11 +3689,18 @@ static int em_dr_write(struct x86_emulate_ctxt *ctxt) > > 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); > - if (ctxt->ops->set_msr(ctxt, reg_read(ctxt, VCPU_REGS_RCX), msr_data)) > + r = ctxt->ops->set_msr(ctxt, msr_index, msr_data); > + > + if (r == X86EMUL_IO_NEEDED) > + return r; > + > + if (r) > return emulate_gp(ctxt, 0); > > return X86EMUL_CONTINUE; > @@ -3701,9 +3708,16 @@ static int em_wrmsr(struct x86_emulate_ctxt *ctxt) > > 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(ctxt, msr_index, &msr_data); > + > + if (r == X86EMUL_IO_NEEDED) > + return r; > > - if (ctxt->ops->get_msr(ctxt, reg_read(ctxt, VCPU_REGS_RCX), &msr_data)) > + if (r) > return emulate_gp(ctxt, 0); > > *reg_write(ctxt, VCPU_REGS_RAX) = (u32)msr_data; > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 88c593f83b28..24c72250f6df 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -1549,12 +1549,75 @@ int kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data) > } > EXPORT_SYMBOL_GPL(kvm_set_msr); > > +static int complete_emulated_msr(struct kvm_vcpu *vcpu, bool is_read) > +{ > + BUG_ON(!vcpu->arch.pending_user_msr); > + > + if (vcpu->run->msr.error) { > + kvm_inject_gp(vcpu, 0); > + } else if (is_read) { > + kvm_rax_write(vcpu, (u32)vcpu->run->msr.data); > + kvm_rdx_write(vcpu, vcpu->run->msr.data >> 32); > + } > + > + return kvm_skip_emulated_instruction(vcpu); > +} > + > +static int complete_emulated_rdmsr(struct kvm_vcpu *vcpu) > +{ > + return complete_emulated_msr(vcpu, true); > +} > + > +static int complete_emulated_wrmsr(struct kvm_vcpu *vcpu) > +{ > + return complete_emulated_msr(vcpu, false); > +} > + > +static int kvm_get_msr_user_space(struct kvm_vcpu *vcpu, u32 index) > +{ > + if (!vcpu->kvm->arch.user_space_msr_enabled) > + return 0; > + > + vcpu->run->exit_reason = KVM_EXIT_X86_RDMSR; > + vcpu->run->msr.error = 0; > + vcpu->run->msr.index = index; > + vcpu->arch.pending_user_msr = true; > + vcpu->arch.complete_userspace_io = complete_emulated_rdmsr; > + > + return 1; > +} > + > +static int kvm_set_msr_user_space(struct kvm_vcpu *vcpu, u32 index, u64 data) > +{ > + if (!vcpu->kvm->arch.user_space_msr_enabled) > + return 0; > + > + vcpu->run->exit_reason = KVM_EXIT_X86_WRMSR; > + vcpu->run->msr.error = 0; > + vcpu->run->msr.index = index; > + vcpu->run->msr.data = data; > + vcpu->arch.pending_user_msr = true; > + vcpu->arch.complete_userspace_io = complete_emulated_wrmsr; I'm probably missing something but where do we reset vcpu->arch.pending_user_msr? Shouldn't it be done in complete_emulated_msr()? > + > + return 1; > +} > + > int kvm_emulate_rdmsr(struct kvm_vcpu *vcpu) > { > u32 ecx = kvm_rcx_read(vcpu); > u64 data; > + int r; > + > + r = kvm_get_msr(vcpu, ecx, &data); > > - if (kvm_get_msr(vcpu, ecx, &data)) { > + /* MSR read failed? See if we should ask user space */ > + if (r && kvm_get_msr_user_space(vcpu, ecx)) { > + /* Bounce to user space */ > + return 0; > + } > + > + /* MSR read failed? Inject a #GP */ > + if (r) { > trace_kvm_msr_read_ex(ecx); > kvm_inject_gp(vcpu, 0); > return 1; > @@ -1572,8 +1635,18 @@ int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu) > { > u32 ecx = kvm_rcx_read(vcpu); > u64 data = kvm_read_edx_eax(vcpu); > + int r; > + > + r = kvm_set_msr(vcpu, ecx, data); > > - if (kvm_set_msr(vcpu, ecx, data)) { > + /* MSR write failed? See if we should ask user space */ > + if (r && kvm_set_msr_user_space(vcpu, ecx, data)) { > + /* Bounce to user space */ > + return 0; > + } > + > + /* MSR write failed? Inject a #GP */ > + if (r) { > trace_kvm_msr_write_ex(ecx, data); > kvm_inject_gp(vcpu, 0); > return 1; > @@ -3476,6 +3549,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) > case KVM_CAP_MSR_PLATFORM_INFO: > case KVM_CAP_EXCEPTION_PAYLOAD: > case KVM_CAP_SET_GUEST_DEBUG: > + case KVM_CAP_X86_USER_SPACE_MSR: > r = 1; > break; > case KVM_CAP_SYNC_REGS: > @@ -4990,6 +5064,10 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, > kvm->arch.exception_payload_enabled = cap->args[0]; > r = 0; > break; > + case KVM_CAP_X86_USER_SPACE_MSR: > + kvm->arch.user_space_msr_enabled = cap->args[0]; > + r = 0; > + break; > default: > r = -EINVAL; > break; > @@ -6319,13 +6397,33 @@ static void emulator_set_segment(struct x86_emulate_ctxt *ctxt, u16 selector, > static int emulator_get_msr(struct x86_emulate_ctxt *ctxt, > u32 msr_index, u64 *pdata) > { > - return kvm_get_msr(emul_to_vcpu(ctxt), msr_index, pdata); > + struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt); > + int r; > + > + r = kvm_get_msr(vcpu, msr_index, pdata); > + > + if (r && kvm_get_msr_user_space(vcpu, msr_index)) { > + /* Bounce to user space */ > + return X86EMUL_IO_NEEDED; > + } > + > + return r; > } > > static int emulator_set_msr(struct x86_emulate_ctxt *ctxt, > u32 msr_index, u64 data) > { > - return kvm_set_msr(emul_to_vcpu(ctxt), msr_index, data); > + struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt); > + int r; > + > + r = kvm_set_msr(emul_to_vcpu(ctxt), msr_index, data); > + > + if (r && kvm_set_msr_user_space(vcpu, msr_index, data)) { > + /* Bounce to user space */ > + return X86EMUL_IO_NEEDED; > + } > + > + return r; > } > > static u64 emulator_get_smbase(struct x86_emulate_ctxt *ctxt) > diff --git a/include/trace/events/kvm.h b/include/trace/events/kvm.h > index 9417a34aad08..26cfb0fa8e7e 100644 > --- a/include/trace/events/kvm.h > +++ b/include/trace/events/kvm.h > @@ -17,7 +17,7 @@ > ERSN(NMI), ERSN(INTERNAL_ERROR), ERSN(OSI), ERSN(PAPR_HCALL), \ > ERSN(S390_UCONTROL), ERSN(WATCHDOG), ERSN(S390_TSCH), ERSN(EPR),\ > ERSN(SYSTEM_EVENT), ERSN(S390_STSI), ERSN(IOAPIC_EOI), \ > - ERSN(HYPERV), ERSN(ARM_NISV) > + ERSN(HYPERV), ERSN(ARM_NISV), ERSN(X86_RDMSR), ERSN(X86_WRMSR) > > TRACE_EVENT(kvm_userspace_exit, > TP_PROTO(__u32 reason, int errno), > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > index 4fdf30316582..13fc7de1eb50 100644 > --- a/include/uapi/linux/kvm.h > +++ b/include/uapi/linux/kvm.h > @@ -248,6 +248,8 @@ struct kvm_hyperv_exit { > #define KVM_EXIT_IOAPIC_EOI 26 > #define KVM_EXIT_HYPERV 27 > #define KVM_EXIT_ARM_NISV 28 > +#define KVM_EXIT_X86_RDMSR 29 > +#define KVM_EXIT_X86_WRMSR 30 > > /* For KVM_EXIT_INTERNAL_ERROR */ > /* Emulate instruction failed. */ > @@ -412,6 +414,13 @@ struct kvm_run { > __u64 esr_iss; > __u64 fault_ipa; > } arm_nisv; > + /* KVM_EXIT_X86_RDMSR / KVM_EXIT_X86_WRMSR */ > + struct { > + __u8 error; > + __u8 pad[3]; > + __u32 index; > + __u64 data; > + } msr; > /* Fix the size of the union. */ > char padding[256]; > }; > @@ -1031,6 +1040,7 @@ struct kvm_ppc_resize_hpt { > #define KVM_CAP_PPC_SECURE_GUEST 181 > #define KVM_CAP_HALT_POLL 182 > #define KVM_CAP_ASYNC_PF_INT 183 > +#define KVM_CAP_X86_USER_SPACE_MSR 184 > > #ifdef KVM_CAP_IRQ_ROUTING
On 03.08.20 13:27, Vitaly Kuznetsov wrote: > Alexander Graf <graf@amazon.com> writes: > >> MSRs are weird. Some of them are normal control registers, such as EFER. >> Some however are registers that really are model specific, not very >> interesting to virtualization workloads, and not performance critical. >> Others again are really just windows into package configuration. >> >> Out of these MSRs, only the first category is necessary to implement in >> kernel space. Rarely accessed MSRs, MSRs that should be fine tunes against >> certain CPU models and MSRs that contain information on the package level >> are much better suited for user space to process. However, over time we have >> accumulated a lot of MSRs that are not the first category, but still handled >> by in-kernel KVM code. >> >> This patch adds a generic interface to handle WRMSR and RDMSR from user >> space. With this, any future MSR that is part of the latter categories can >> be handled in user space. >> >> Furthermore, it allows us to replace the existing "ignore_msrs" logic with >> something that applies per-VM rather than on the full system. That way you >> can run productive VMs in parallel to experimental ones where you don't care >> about proper MSR handling. >> >> Signed-off-by: Alexander Graf <graf@amazon.com> >> >> --- >> >> v1 -> v2: >> >> - s/ETRAP_TO_USER_SPACE/ENOENT/g >> - deflect all #GP injection events to user space, not just unknown MSRs. >> That was we can also deflect allowlist errors later >> - fix emulator case >> >> v2 -> v3: >> >> - return r if r == X86EMUL_IO_NEEDED >> - s/KVM_EXIT_RDMSR/KVM_EXIT_X86_RDMSR/g >> - s/KVM_EXIT_WRMSR/KVM_EXIT_X86_WRMSR/g >> - Use complete_userspace_io logic instead of reply field >> - Simplify trapping code >> --- >> Documentation/virt/kvm/api.rst | 62 +++++++++++++++++++ >> arch/x86/include/asm/kvm_host.h | 6 ++ >> arch/x86/kvm/emulate.c | 18 +++++- >> arch/x86/kvm/x86.c | 106 ++++++++++++++++++++++++++++++-- >> include/trace/events/kvm.h | 2 +- >> include/uapi/linux/kvm.h | 10 +++ >> 6 files changed, 197 insertions(+), 7 deletions(-) >> >> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst >> index 320788f81a05..79c3e2fdfae4 100644 >> --- a/Documentation/virt/kvm/api.rst >> +++ b/Documentation/virt/kvm/api.rst >> @@ -5155,6 +5155,35 @@ Note that KVM does not skip the faulting instruction as it does for >> KVM_EXIT_MMIO, but userspace has to emulate any change to the processing state >> if it decides to decode and emulate the instruction. >> >> +:: >> + >> + /* KVM_EXIT_X86_RDMSR / KVM_EXIT_X86_WRMSR */ >> + struct { >> + __u8 error; >> + __u8 pad[3]; >> + __u32 index; >> + __u64 data; >> + } msr; >> + >> +Used on x86 systems. When the VM capability KVM_CAP_X86_USER_SPACE_MSR is >> +enabled, MSR accesses to registers that would invoke a #GP by KVM kernel code >> +will instead trigger a KVM_EXIT_X86_RDMSR exit for reads and KVM_EXIT_X86_WRMSR >> +exit for writes. >> + >> +For KVM_EXIT_X86_RDMSR, the "index" field tells user space which MSR the guest >> +wants to read. To respond to this request with a successful read, user space >> +writes the respective data into the "data" field and must continue guest >> +execution to ensure the read data is transferred into guest register state. >> + >> +If the RDMSR request was unsuccessful, user space indicates that with a "1" in >> +the "error" field. This will inject a #GP into the guest when the VCPU is >> +executed again. >> + >> +For KVM_EXIT_X86_WRMSR, the "index" field tells user space which MSR the guest >> +wants to write. Once finished processing the event, user space must continue >> +vCPU execution. If the MSR write was unsuccessful, user space also sets the >> +"error" field to "1". >> + >> :: >> >> /* Fix the size of the union. */ >> @@ -5844,6 +5873,28 @@ controlled by the kvm module parameter halt_poll_ns. This capability allows >> the maximum halt time to specified on a per-VM basis, effectively overriding >> the module parameter for the target VM. >> >> +7.21 KVM_CAP_X86_USER_SPACE_MSR >> +------------------------------- >> + >> +:Architectures: x86 >> +:Target: VM >> +:Parameters: args[0] is 1 if user space MSR handling is enabled, 0 otherwise >> +:Returns: 0 on success; -1 on error >> + >> +This capability enables trapping of #GP invoking RDMSR and WRMSR instructions >> +into user space. >> + >> +When a guest requests to read or write an MSR, KVM may not implement all MSRs >> +that are relevant to a respective system. It also does not differentiate by >> +CPU type. >> + >> +To allow more fine grained control over MSR handling, user space may enable >> +this capability. With it enabled, MSR accesses that would usually trigger >> +a #GP event inside the guest by KVM will instead trigger KVM_EXIT_X86_RDMSR >> +and KVM_EXIT_X86_WRMSR exit notifications which user space can then handle to >> +implement model specific MSR handling and/or user notifications to inform >> +a user that an MSR was not handled. >> + >> 8. Other capabilities. >> ====================== >> >> @@ -6151,3 +6202,14 @@ KVM can therefore start protected VMs. >> This capability governs the KVM_S390_PV_COMMAND ioctl and the >> KVM_MP_STATE_LOAD MP_STATE. KVM_SET_MP_STATE can fail for protected >> guests when the state change is invalid. >> + >> +8.24 KVM_CAP_X86_USER_SPACE_MSR >> +---------------------------- >> + >> +:Architectures: x86 >> + >> +This capability indicates that KVM supports deflection of MSR reads and >> +writes to user space. It can be enabled on a VM level. If enabled, MSR >> +accesses that would usually trigger a #GP by KVM into the guest will >> +instead get bounced to user space through the KVM_EXIT_X86_RDMSR and >> +KVM_EXIT_X86_WRMSR exit notifications. >> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h >> index be5363b21540..809eed0dbdea 100644 >> --- a/arch/x86/include/asm/kvm_host.h >> +++ b/arch/x86/include/asm/kvm_host.h >> @@ -829,6 +829,9 @@ struct kvm_vcpu_arch { >> >> /* AMD MSRC001_0015 Hardware Configuration */ >> u64 msr_hwcr; >> + >> + /* User space is handling an MSR request */ >> + bool pending_user_msr; >> }; >> >> struct kvm_lpage_info { >> @@ -1002,6 +1005,9 @@ struct kvm_arch { >> bool guest_can_read_msr_platform_info; >> bool exception_payload_enabled; >> >> + /* Deflect RDMSR and WRMSR to user space when they trigger a #GP */ >> + bool user_space_msr_enabled; >> + >> struct kvm_pmu_event_filter *pmu_event_filter; >> struct task_struct *nx_lpage_recovery_thread; >> }; >> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c >> index d0e2825ae617..744ab9c92b73 100644 >> --- a/arch/x86/kvm/emulate.c >> +++ b/arch/x86/kvm/emulate.c >> @@ -3689,11 +3689,18 @@ static int em_dr_write(struct x86_emulate_ctxt *ctxt) >> >> 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); >> - if (ctxt->ops->set_msr(ctxt, reg_read(ctxt, VCPU_REGS_RCX), msr_data)) >> + r = ctxt->ops->set_msr(ctxt, msr_index, msr_data); >> + >> + if (r == X86EMUL_IO_NEEDED) >> + return r; >> + >> + if (r) >> return emulate_gp(ctxt, 0); >> >> return X86EMUL_CONTINUE; >> @@ -3701,9 +3708,16 @@ static int em_wrmsr(struct x86_emulate_ctxt *ctxt) >> >> 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(ctxt, msr_index, &msr_data); >> + >> + if (r == X86EMUL_IO_NEEDED) >> + return r; >> >> - if (ctxt->ops->get_msr(ctxt, reg_read(ctxt, VCPU_REGS_RCX), &msr_data)) >> + if (r) >> return emulate_gp(ctxt, 0); >> >> *reg_write(ctxt, VCPU_REGS_RAX) = (u32)msr_data; >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index 88c593f83b28..24c72250f6df 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -1549,12 +1549,75 @@ int kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data) >> } >> EXPORT_SYMBOL_GPL(kvm_set_msr); >> >> +static int complete_emulated_msr(struct kvm_vcpu *vcpu, bool is_read) >> +{ >> + BUG_ON(!vcpu->arch.pending_user_msr); >> + >> + if (vcpu->run->msr.error) { >> + kvm_inject_gp(vcpu, 0); >> + } else if (is_read) { >> + kvm_rax_write(vcpu, (u32)vcpu->run->msr.data); >> + kvm_rdx_write(vcpu, vcpu->run->msr.data >> 32); >> + } >> + >> + return kvm_skip_emulated_instruction(vcpu); >> +} >> + >> +static int complete_emulated_rdmsr(struct kvm_vcpu *vcpu) >> +{ >> + return complete_emulated_msr(vcpu, true); >> +} >> + >> +static int complete_emulated_wrmsr(struct kvm_vcpu *vcpu) >> +{ >> + return complete_emulated_msr(vcpu, false); >> +} >> + >> +static int kvm_get_msr_user_space(struct kvm_vcpu *vcpu, u32 index) >> +{ >> + if (!vcpu->kvm->arch.user_space_msr_enabled) >> + return 0; >> + >> + vcpu->run->exit_reason = KVM_EXIT_X86_RDMSR; >> + vcpu->run->msr.error = 0; >> + vcpu->run->msr.index = index; >> + vcpu->arch.pending_user_msr = true; >> + vcpu->arch.complete_userspace_io = complete_emulated_rdmsr; >> + >> + return 1; >> +} >> + >> +static int kvm_set_msr_user_space(struct kvm_vcpu *vcpu, u32 index, u64 data) >> +{ >> + if (!vcpu->kvm->arch.user_space_msr_enabled) >> + return 0; >> + >> + vcpu->run->exit_reason = KVM_EXIT_X86_WRMSR; >> + vcpu->run->msr.error = 0; >> + vcpu->run->msr.index = index; >> + vcpu->run->msr.data = data; >> + vcpu->arch.pending_user_msr = true; >> + vcpu->arch.complete_userspace_io = complete_emulated_wrmsr; > > I'm probably missing something but where do we reset > vcpu->arch.pending_user_msr? Shouldn't it be done in > complete_emulated_msr()? It's even worse than that: We don't need it at all. I'll remove it for v4. Alex Amazon Development Center Germany GmbH Krausenstr. 38 10117 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B Sitz: Berlin Ust-ID: DE 289 237 879
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 320788f81a05..79c3e2fdfae4 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -5155,6 +5155,35 @@ Note that KVM does not skip the faulting instruction as it does for KVM_EXIT_MMIO, but userspace has to emulate any change to the processing state if it decides to decode and emulate the instruction. +:: + + /* KVM_EXIT_X86_RDMSR / KVM_EXIT_X86_WRMSR */ + struct { + __u8 error; + __u8 pad[3]; + __u32 index; + __u64 data; + } msr; + +Used on x86 systems. When the VM capability KVM_CAP_X86_USER_SPACE_MSR is +enabled, MSR accesses to registers that would invoke a #GP by KVM kernel code +will instead trigger a KVM_EXIT_X86_RDMSR exit for reads and KVM_EXIT_X86_WRMSR +exit for writes. + +For KVM_EXIT_X86_RDMSR, the "index" field tells user space which MSR the guest +wants to read. To respond to this request with a successful read, user space +writes the respective data into the "data" field and must continue guest +execution to ensure the read data is transferred into guest register state. + +If the RDMSR request was unsuccessful, user space indicates that with a "1" in +the "error" field. This will inject a #GP into the guest when the VCPU is +executed again. + +For KVM_EXIT_X86_WRMSR, the "index" field tells user space which MSR the guest +wants to write. Once finished processing the event, user space must continue +vCPU execution. If the MSR write was unsuccessful, user space also sets the +"error" field to "1". + :: /* Fix the size of the union. */ @@ -5844,6 +5873,28 @@ controlled by the kvm module parameter halt_poll_ns. This capability allows the maximum halt time to specified on a per-VM basis, effectively overriding the module parameter for the target VM. +7.21 KVM_CAP_X86_USER_SPACE_MSR +------------------------------- + +:Architectures: x86 +:Target: VM +:Parameters: args[0] is 1 if user space MSR handling is enabled, 0 otherwise +:Returns: 0 on success; -1 on error + +This capability enables trapping of #GP invoking RDMSR and WRMSR instructions +into user space. + +When a guest requests to read or write an MSR, KVM may not implement all MSRs +that are relevant to a respective system. It also does not differentiate by +CPU type. + +To allow more fine grained control over MSR handling, user space may enable +this capability. With it enabled, MSR accesses that would usually trigger +a #GP event inside the guest by KVM will instead trigger KVM_EXIT_X86_RDMSR +and KVM_EXIT_X86_WRMSR exit notifications which user space can then handle to +implement model specific MSR handling and/or user notifications to inform +a user that an MSR was not handled. + 8. Other capabilities. ====================== @@ -6151,3 +6202,14 @@ KVM can therefore start protected VMs. This capability governs the KVM_S390_PV_COMMAND ioctl and the KVM_MP_STATE_LOAD MP_STATE. KVM_SET_MP_STATE can fail for protected guests when the state change is invalid. + +8.24 KVM_CAP_X86_USER_SPACE_MSR +---------------------------- + +:Architectures: x86 + +This capability indicates that KVM supports deflection of MSR reads and +writes to user space. It can be enabled on a VM level. If enabled, MSR +accesses that would usually trigger a #GP by KVM into the guest will +instead get bounced to user space through the KVM_EXIT_X86_RDMSR and +KVM_EXIT_X86_WRMSR exit notifications. diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index be5363b21540..809eed0dbdea 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -829,6 +829,9 @@ struct kvm_vcpu_arch { /* AMD MSRC001_0015 Hardware Configuration */ u64 msr_hwcr; + + /* User space is handling an MSR request */ + bool pending_user_msr; }; struct kvm_lpage_info { @@ -1002,6 +1005,9 @@ struct kvm_arch { bool guest_can_read_msr_platform_info; bool exception_payload_enabled; + /* Deflect RDMSR and WRMSR to user space when they trigger a #GP */ + bool user_space_msr_enabled; + struct kvm_pmu_event_filter *pmu_event_filter; struct task_struct *nx_lpage_recovery_thread; }; diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index d0e2825ae617..744ab9c92b73 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -3689,11 +3689,18 @@ static int em_dr_write(struct x86_emulate_ctxt *ctxt) 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); - if (ctxt->ops->set_msr(ctxt, reg_read(ctxt, VCPU_REGS_RCX), msr_data)) + r = ctxt->ops->set_msr(ctxt, msr_index, msr_data); + + if (r == X86EMUL_IO_NEEDED) + return r; + + if (r) return emulate_gp(ctxt, 0); return X86EMUL_CONTINUE; @@ -3701,9 +3708,16 @@ static int em_wrmsr(struct x86_emulate_ctxt *ctxt) 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(ctxt, msr_index, &msr_data); + + if (r == X86EMUL_IO_NEEDED) + return r; - if (ctxt->ops->get_msr(ctxt, reg_read(ctxt, VCPU_REGS_RCX), &msr_data)) + if (r) return emulate_gp(ctxt, 0); *reg_write(ctxt, VCPU_REGS_RAX) = (u32)msr_data; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 88c593f83b28..24c72250f6df 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1549,12 +1549,75 @@ int kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data) } EXPORT_SYMBOL_GPL(kvm_set_msr); +static int complete_emulated_msr(struct kvm_vcpu *vcpu, bool is_read) +{ + BUG_ON(!vcpu->arch.pending_user_msr); + + if (vcpu->run->msr.error) { + kvm_inject_gp(vcpu, 0); + } else if (is_read) { + kvm_rax_write(vcpu, (u32)vcpu->run->msr.data); + kvm_rdx_write(vcpu, vcpu->run->msr.data >> 32); + } + + return kvm_skip_emulated_instruction(vcpu); +} + +static int complete_emulated_rdmsr(struct kvm_vcpu *vcpu) +{ + return complete_emulated_msr(vcpu, true); +} + +static int complete_emulated_wrmsr(struct kvm_vcpu *vcpu) +{ + return complete_emulated_msr(vcpu, false); +} + +static int kvm_get_msr_user_space(struct kvm_vcpu *vcpu, u32 index) +{ + if (!vcpu->kvm->arch.user_space_msr_enabled) + return 0; + + vcpu->run->exit_reason = KVM_EXIT_X86_RDMSR; + vcpu->run->msr.error = 0; + vcpu->run->msr.index = index; + vcpu->arch.pending_user_msr = true; + vcpu->arch.complete_userspace_io = complete_emulated_rdmsr; + + return 1; +} + +static int kvm_set_msr_user_space(struct kvm_vcpu *vcpu, u32 index, u64 data) +{ + if (!vcpu->kvm->arch.user_space_msr_enabled) + return 0; + + vcpu->run->exit_reason = KVM_EXIT_X86_WRMSR; + vcpu->run->msr.error = 0; + vcpu->run->msr.index = index; + vcpu->run->msr.data = data; + vcpu->arch.pending_user_msr = true; + vcpu->arch.complete_userspace_io = complete_emulated_wrmsr; + + return 1; +} + int kvm_emulate_rdmsr(struct kvm_vcpu *vcpu) { u32 ecx = kvm_rcx_read(vcpu); u64 data; + int r; + + r = kvm_get_msr(vcpu, ecx, &data); - if (kvm_get_msr(vcpu, ecx, &data)) { + /* MSR read failed? See if we should ask user space */ + if (r && kvm_get_msr_user_space(vcpu, ecx)) { + /* Bounce to user space */ + return 0; + } + + /* MSR read failed? Inject a #GP */ + if (r) { trace_kvm_msr_read_ex(ecx); kvm_inject_gp(vcpu, 0); return 1; @@ -1572,8 +1635,18 @@ int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu) { u32 ecx = kvm_rcx_read(vcpu); u64 data = kvm_read_edx_eax(vcpu); + int r; + + r = kvm_set_msr(vcpu, ecx, data); - if (kvm_set_msr(vcpu, ecx, data)) { + /* MSR write failed? See if we should ask user space */ + if (r && kvm_set_msr_user_space(vcpu, ecx, data)) { + /* Bounce to user space */ + return 0; + } + + /* MSR write failed? Inject a #GP */ + if (r) { trace_kvm_msr_write_ex(ecx, data); kvm_inject_gp(vcpu, 0); return 1; @@ -3476,6 +3549,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_MSR_PLATFORM_INFO: case KVM_CAP_EXCEPTION_PAYLOAD: case KVM_CAP_SET_GUEST_DEBUG: + case KVM_CAP_X86_USER_SPACE_MSR: r = 1; break; case KVM_CAP_SYNC_REGS: @@ -4990,6 +5064,10 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, kvm->arch.exception_payload_enabled = cap->args[0]; r = 0; break; + case KVM_CAP_X86_USER_SPACE_MSR: + kvm->arch.user_space_msr_enabled = cap->args[0]; + r = 0; + break; default: r = -EINVAL; break; @@ -6319,13 +6397,33 @@ static void emulator_set_segment(struct x86_emulate_ctxt *ctxt, u16 selector, static int emulator_get_msr(struct x86_emulate_ctxt *ctxt, u32 msr_index, u64 *pdata) { - return kvm_get_msr(emul_to_vcpu(ctxt), msr_index, pdata); + struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt); + int r; + + r = kvm_get_msr(vcpu, msr_index, pdata); + + if (r && kvm_get_msr_user_space(vcpu, msr_index)) { + /* Bounce to user space */ + return X86EMUL_IO_NEEDED; + } + + return r; } static int emulator_set_msr(struct x86_emulate_ctxt *ctxt, u32 msr_index, u64 data) { - return kvm_set_msr(emul_to_vcpu(ctxt), msr_index, data); + struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt); + int r; + + r = kvm_set_msr(emul_to_vcpu(ctxt), msr_index, data); + + if (r && kvm_set_msr_user_space(vcpu, msr_index, data)) { + /* Bounce to user space */ + return X86EMUL_IO_NEEDED; + } + + return r; } static u64 emulator_get_smbase(struct x86_emulate_ctxt *ctxt) diff --git a/include/trace/events/kvm.h b/include/trace/events/kvm.h index 9417a34aad08..26cfb0fa8e7e 100644 --- a/include/trace/events/kvm.h +++ b/include/trace/events/kvm.h @@ -17,7 +17,7 @@ ERSN(NMI), ERSN(INTERNAL_ERROR), ERSN(OSI), ERSN(PAPR_HCALL), \ ERSN(S390_UCONTROL), ERSN(WATCHDOG), ERSN(S390_TSCH), ERSN(EPR),\ ERSN(SYSTEM_EVENT), ERSN(S390_STSI), ERSN(IOAPIC_EOI), \ - ERSN(HYPERV), ERSN(ARM_NISV) + ERSN(HYPERV), ERSN(ARM_NISV), ERSN(X86_RDMSR), ERSN(X86_WRMSR) TRACE_EVENT(kvm_userspace_exit, TP_PROTO(__u32 reason, int errno), diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 4fdf30316582..13fc7de1eb50 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -248,6 +248,8 @@ struct kvm_hyperv_exit { #define KVM_EXIT_IOAPIC_EOI 26 #define KVM_EXIT_HYPERV 27 #define KVM_EXIT_ARM_NISV 28 +#define KVM_EXIT_X86_RDMSR 29 +#define KVM_EXIT_X86_WRMSR 30 /* For KVM_EXIT_INTERNAL_ERROR */ /* Emulate instruction failed. */ @@ -412,6 +414,13 @@ struct kvm_run { __u64 esr_iss; __u64 fault_ipa; } arm_nisv; + /* KVM_EXIT_X86_RDMSR / KVM_EXIT_X86_WRMSR */ + struct { + __u8 error; + __u8 pad[3]; + __u32 index; + __u64 data; + } msr; /* Fix the size of the union. */ char padding[256]; }; @@ -1031,6 +1040,7 @@ struct kvm_ppc_resize_hpt { #define KVM_CAP_PPC_SECURE_GUEST 181 #define KVM_CAP_HALT_POLL 182 #define KVM_CAP_ASYNC_PF_INT 183 +#define KVM_CAP_X86_USER_SPACE_MSR 184 #ifdef KVM_CAP_IRQ_ROUTING
MSRs are weird. Some of them are normal control registers, such as EFER. Some however are registers that really are model specific, not very interesting to virtualization workloads, and not performance critical. Others again are really just windows into package configuration. Out of these MSRs, only the first category is necessary to implement in kernel space. Rarely accessed MSRs, MSRs that should be fine tunes against certain CPU models and MSRs that contain information on the package level are much better suited for user space to process. However, over time we have accumulated a lot of MSRs that are not the first category, but still handled by in-kernel KVM code. This patch adds a generic interface to handle WRMSR and RDMSR from user space. With this, any future MSR that is part of the latter categories can be handled in user space. Furthermore, it allows us to replace the existing "ignore_msrs" logic with something that applies per-VM rather than on the full system. That way you can run productive VMs in parallel to experimental ones where you don't care about proper MSR handling. Signed-off-by: Alexander Graf <graf@amazon.com> --- v1 -> v2: - s/ETRAP_TO_USER_SPACE/ENOENT/g - deflect all #GP injection events to user space, not just unknown MSRs. That was we can also deflect allowlist errors later - fix emulator case v2 -> v3: - return r if r == X86EMUL_IO_NEEDED - s/KVM_EXIT_RDMSR/KVM_EXIT_X86_RDMSR/g - s/KVM_EXIT_WRMSR/KVM_EXIT_X86_WRMSR/g - Use complete_userspace_io logic instead of reply field - Simplify trapping code --- Documentation/virt/kvm/api.rst | 62 +++++++++++++++++++ arch/x86/include/asm/kvm_host.h | 6 ++ arch/x86/kvm/emulate.c | 18 +++++- arch/x86/kvm/x86.c | 106 ++++++++++++++++++++++++++++++-- include/trace/events/kvm.h | 2 +- include/uapi/linux/kvm.h | 10 +++ 6 files changed, 197 insertions(+), 7 deletions(-)