It is intended to be used only during startup, typically by a launcher
that is aware which MSRs should be emulated as no-ops.
On Wed, Oct 28, 2009 at 2:28 PM, Richard Winthers <rwinthers@xxxxxxxxx> wrote:
> Is this interface supposed to support changing MSR handing at runtime or is
> the ioctl only meant to be called prior to KVM_RUN?
> Thanks,
> Richard
> On Wed, Oct 28, 2009 at 1:23 PM, David Windsor <dwindsor@xxxxxxxxx> wrote:
>>
>> Hi,
>>
>> I've encountered a situation in which I would like to allow userspace
>> to set the MSRs which KVM should not emulate and instead implement
>> these as no-ops.
>>
>> I have not seen any work in this space, furthermore there is an item
>> on the KVM TODO that is very similar to what I'm trying to do.
>>
>> The userspace interface is an extension of kvm_vcpu_ioctl, adding the
>> KVM_SET_MSRS_NOOP flag. It takes a struct kvm_msrs as a list of which
>> MSRs should be no-ops and adds the field noop to struct kvm_msr_entry.
>> This patch only affects vmx, but if the approach is sane, I can
>> extend it to support svm as well.
>>
>>
>>
>> diff -purN linux-2.6.32-rc5/arch/x86/include/asm/kvm.h
>> linux-2.6.32-rc5-kvm-msrs-noop/arch/x86/include/asm/kvm.h
>> --- linux-2.6.32-rc5/arch/x86/include/asm/kvm.h 2009-10-15
>> 20:41:50.000000000 -0400
>> +++ linux-2.6.32-rc5-kvm-msrs-noop/arch/x86/include/asm/kvm.h 2009-10-27
>> 22:44:58.000000000 -0400
>> @@ -144,6 +144,7 @@ struct kvm_msr_entry {
>> __u32 index;
>> __u32 reserved;
>> __u64 data;
>> + __u8 noop;
>> };
>>
>> /* for KVM_GET_MSRS and KVM_SET_MSRS */
>> diff -purN linux-2.6.32-rc5/arch/x86/include/asm/kvm_host.h
>> linux-2.6.32-rc5-kvm-msrs-noop/arch/x86/include/asm/kvm_host.h
>> --- linux-2.6.32-rc5/arch/x86/include/asm/kvm_host.h 2009-10-15
>> 20:41:50.000000000 -0400
>> +++ linux-2.6.32-rc5-kvm-msrs-noop/arch/x86/include/asm/kvm_host.h
>> 2009-10-27
>> 22:44:58.000000000 -0400
>> @@ -481,6 +481,7 @@ struct kvm_x86_ops {
>> struct kvm_guest_debug *dbg);
>> int (*get_msr)(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata);
>> int (*set_msr)(struct kvm_vcpu *vcpu, u32 msr_index, u64 data);
>> + int (*set_msr_noop)(struct kvm_vcpu *vcpu, u32 msr_index);
>> u64 (*get_segment_base)(struct kvm_vcpu *vcpu, int seg);
>> void (*get_segment)(struct kvm_vcpu *vcpu,
>> struct kvm_segment *var, int seg);
>> diff -purN linux-2.6.32-rc5/arch/x86/kvm/vmx.c
>> linux-2.6.32-rc5-kvm-msrs-noop/arch/x86/kvm/vmx.c
>> --- linux-2.6.32-rc5/arch/x86/kvm/vmx.c 2009-10-15 20:41:50.000000000
>> -0400
>> +++ linux-2.6.32-rc5-kvm-msrs-noop/arch/x86/kvm/vmx.c 2009-10-27
>> 22:44:58.000000000 -0400
>> @@ -983,6 +983,13 @@ static int vmx_get_msr(struct kvm_vcpu *
>> return -EINVAL;
>> }
>>
>> + msr = find_msr_entry(to_vmx(vcpu), msr_index);
>> + if (msr) {
>> + if (msr->noop) {
>> + return 0;
>> + }
>> + }
>> +
>> switch (msr_index) {
>> #ifdef CONFIG_X86_64
>> case MSR_FS_BASE:
>> @@ -1032,6 +1039,13 @@ static int vmx_set_msr(struct kvm_vcpu *
>> u64 host_tsc;
>> int ret = 0;
>>
>> + msr = find_msr_entry(to_vmx(vcpu), msr_index);
>> + if (msr) {
>> + if (msr->noop) {
>> + return ret;
>> + }
>> + }
>> +
>> switch (msr_index) {
>> case MSR_EFER:
>> vmx_load_host_state(vmx);
>> @@ -1078,6 +1092,21 @@ static int vmx_set_msr(struct kvm_vcpu *
>> return ret;
>> }
>>
>> +static int vmx_set_msr_noop(struct kvm_vcpu *vcpu, u32 msr)
>> +{
>> + struct kvm_msr_entry *m;
>> +
>> + if (!vcpu)
>> + return -1;
>> +
>> + m = find_msr_entry(to_vmx(vcpu), msr);
>> + if (!m)
>> + return -1;
>> +
>> + m->noop = 1;
>> + return 0;
>> +}
>> +
>> static void vmx_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)
>> {
>> __set_bit(reg, (unsigned long *)&vcpu->arch.regs_avail);
>> @@ -3942,6 +3971,7 @@ static struct kvm_x86_ops vmx_x86_ops =
>> .set_guest_debug = set_guest_debug,
>> .get_msr = vmx_get_msr,
>> .set_msr = vmx_set_msr,
>> + .set_msr_noop = vmx_set_msr_noop,
>> .get_segment_base = vmx_get_segment_base,
>> .get_segment = vmx_get_segment,
>> .set_segment = vmx_set_segment,
>> diff -purN linux-2.6.32-rc5/arch/x86/kvm/x86.c
>> linux-2.6.32-rc5-kvm-msrs-noop/arch/x86/kvm/x86.c
>> --- linux-2.6.32-rc5/arch/x86/kvm/x86.c 2009-10-15 20:41:50.000000000
>> -0400
>> +++ linux-2.6.32-rc5-kvm-msrs-noop/arch/x86/kvm/x86.c 2009-10-27
>> 22:44:58.000000000 -0400
>> @@ -975,6 +975,31 @@ int kvm_get_msr(struct kvm_vcpu *vcpu, u
>> return kvm_x86_ops->get_msr(vcpu, msr_index, pdata);
>> }
>>
>> +static int kvm_set_msrs_noop(struct kvm_vcpu *vcpu, struct kvm_msrs
>> __user *user_msrs)
>> +{
>> + int i, r;
>> + int size;
>> + struct kvm_msrs msrs;
>> + struct kvm_msr_entry *entries;
>> +
>> + if (copy_from_user(&msrs, user_msrs, sizeof msrs))
>> + goto out;
>> +
>> + size = sizeof(struct kvm_msr_entry) * msrs.nmsrs;
>> + if (copy_from_user(entries, user_msrs->entries, size))
>> + goto out;
>> +
>> + for (i = 0; i < msrs.nmsrs; i++) {
>> + r = kvm_x86_ops->set_msr_noop(vcpu, entries[i].index);
>> + if (r)
>> + goto out;
>> + }
>> +
>> + return 0;
>> +out:
>> + return -1;
>> +}
>> +
>> static int get_msr_mtrr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
>> {
>> u64 *p = (u64 *)&vcpu->arch.mtrr_state.fixed_ranges;
>> @@ -1864,6 +1889,9 @@ long kvm_arch_vcpu_ioctl(struct file *fi
>> case KVM_SET_MSRS:
>> r = msr_io(vcpu, argp, do_set_msr, 0);
>> break;
>> + case KVM_SET_MSRS_NOOP:
>> + r = kvm_set_msrs_noop(vcpu, argp);
>> + break;
>> case KVM_TPR_ACCESS_REPORTING: {
>> struct kvm_tpr_access_ctl tac;
>>
>> diff -purN linux-2.6.32-rc5/include/linux/kvm.h
>> linux-2.6.32-rc5-kvm-msrs-noop/include/linux/kvm.h
>> --- linux-2.6.32-rc5/include/linux/kvm.h 2009-10-15
>> 20:41:50.000000000 -0400
>> +++ linux-2.6.32-rc5-kvm-msrs-noop/include/linux/kvm.h 2009-10-27
>> 22:46:36.000000000 -0400
>> @@ -593,6 +593,7 @@ struct kvm_irqfd {
>> #define KVM_X86_SETUP_MCE _IOW(KVMIO, 0x9c, __u64)
>> #define KVM_X86_GET_MCE_CAP_SUPPORTED _IOR(KVMIO, 0x9d, __u64)
>> #define KVM_X86_SET_MCE _IOW(KVMIO, 0x9e, struct kvm_x86_mce)
>> +#define KVM_SET_MSRS_NOOP _IOW(KVMIO, 0x9f, struct kvm_msrs)
>>
>> /*
>> * Deprecated interfaces
>> --
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