On Sun, Feb 18, 2024, Yang Weijiang wrote:
Add CET MSRs to the list of MSRs reported to userspace if the feature,We never resolved the conservation from v6[*], but I still agree with Maxim's
i.e. IBT or SHSTK, associated with the MSRs is supported by KVM.
SSP can only be read via RDSSP. Writing even requires destructive and
potentially faulting operations such as SAVEPREVSSP/RSTORSSP or
SETSSBSY/CLRSSBSY. Let the host use a pseudo-MSR that is just a wrapper
for the GUEST_SSP field of the VMCS.
Suggested-by: Chao Gao <chao.gao@xxxxxxxxx>
Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
---
arch/x86/include/uapi/asm/kvm_para.h | 1 +
arch/x86/kvm/vmx/vmx.c | 2 ++
arch/x86/kvm/x86.c | 18 ++++++++++++++++++
3 files changed, 21 insertions(+)
diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
index 605899594ebb..9d08c0bec477 100644
--- a/arch/x86/include/uapi/asm/kvm_para.h
+++ b/arch/x86/include/uapi/asm/kvm_para.h
@@ -58,6 +58,7 @@
#define MSR_KVM_ASYNC_PF_INT 0x4b564d06
#define MSR_KVM_ASYNC_PF_ACK 0x4b564d07
#define MSR_KVM_MIGRATION_CONTROL 0x4b564d08
+#define MSR_KVM_SSP 0x4b564d09
view that defining a synthetic MSR, which "steals" an MSR from KVM's MSR address
space, is a bad idea.
And I still also think that KVM_SET_ONE_REG is the best way forward. Completely
untested, but I think this is all that is needed to wire up KVM_{G,S}ET_ONE_REG
to support MSRs, and carve out room for 250+ other register types, plus room for
more future stuff as needed.
We'll still need a KVM-defined MSR for SSP, but it can be KVM internal, not uAPI,
e.g. the "index" exposed to userspace can simply be '0' for a register type of
KVM_X86_REG_SYNTHETIC_MSR, and then the translated internal index can be any
value that doesn't conflict.
diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index ef11aa4cab42..ca2a47a85fa1 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -410,6 +410,16 @@ struct kvm_xcrs {
__u64 padding[16];
};
+#define KVM_X86_REG_MSR (1 << 2)
+#define KVM_X86_REG_SYNTHETIC_MSR (1 << 3)
+
+struct kvm_x86_reg_id {
+ __u32 index;
+ __u8 type;
+ __u8 rsvd;
+ __u16 rsvd16;
+};
+
#define KVM_SYNC_X86_REGS (1UL << 0)
#define KVM_SYNC_X86_SREGS (1UL << 1)
#define KVM_SYNC_X86_EVENTS (1UL << 2)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 47d9f03b7778..53f2b43b4651 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2244,6 +2244,30 @@ static int do_set_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
return kvm_set_msr_ignored_check(vcpu, index, *data, true);
}
+static int kvm_get_one_msr(struct kvm_vcpu *vcpu, u32 msr, u64 __user *value)
+{
+ u64 val;
+
+ r = do_get_msr(vcpu, reg.index, &val);
+ if (r)
+ return r;
+
+ if (put_user(val, value);
+ return -EFAULT;
+
+ return 0;
+}
+
+static int kvm_set_one_msr(struct kvm_vcpu *vcpu, u32 msr, u64 __user *value)
+{
+ u64 val;
+
+ if (get_user(val, value);
+ return -EFAULT;
+
+ return do_set_msr(vcpu, reg.index, &val);
+}
+
#ifdef CONFIG_X86_64
struct pvclock_clock {
int vclock_mode;
@@ -5976,6 +6000,39 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
srcu_read_unlock(&vcpu->kvm->srcu, idx);
break;
}
+ case KVM_GET_ONE_REG:
+ case KVM_SET_ONE_REG: {
+ struct kvm_x86_reg_id id;
+ struct kvm_one_reg reg;
+ u64 __user *value;
+
+ r = -EFAULT;
+ if (copy_from_user(®, argp, sizeof(reg)))
+ break;
+
+ r = -EINVAL;
+ id = (struct kvm_x86_reg)reg->id;
+ if (id.rsvd || id.rsvd16)
+ break;
+
+ if (id.type != KVM_X86_REG_MSR &&
+ id.type != KVM_X86_REG_SYNTHETIC_MSR)
+ break;
+
+ if (id.type == KVM_X86_REG_SYNTHETIC_MSR) {
+ id.type = KVM_X86_REG_MSR;
+ r = kvm_translate_synthetic_msr(&id.index);
+ if (r)
+ break;
+ }
+
+ value = u64_to_user_ptr(reg.addr);
+ if (ioctl == KVM_GET_ONE_REG)
+ r = kvm_get_one_msr(vcpu, id.index, value);
+ else
+ r = kvm_set_one_msr(vcpu, id.index, value);
+ break;
+ }
case KVM_TPR_ACCESS_REPORTING: {
struct kvm_tpr_access_ctl tac;