This commit implements an enhanced x86 version of S390
KVM_CAP_SYNC_REGS functionality. KVM_CAP_SYNC_REGS "allow[s]
userspace to access certain guest registers without having
to call SET/GET_*REGS”. This reduces ioctl overhead which
is particularly important when userspace is making synchronous
guest state modifications (e.g. when emulating and/or intercepting
instructions).
Originally implemented upstream for the S390, the x86 differences
follow:
- the capability can be enabled/disabled
- the register sets to be copied out out to kvm_run are selectable
by userspace
- vcpu_events and selectable MSRs are available in addition to the
basic register sets (regs, sregs, debug_regs, and fpu).
Signed-off-by: Ken Hofsass <hofsass@xxxxxxxxxx>
---
Documentation/virtual/kvm/api.txt | 49 ++++++++++++++
arch/x86/include/uapi/asm/kvm.h | 32 ++++++++-
arch/x86/kvm/x86.c | 134 +++++++++++++++++++++++++++++++++++++-
include/uapi/linux/kvm.h | 6 +-
4 files changed, 216 insertions(+), 5 deletions(-)
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index e63a35fafef0..9536eb310d04 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -3951,6 +3951,55 @@ Once this is done the KVM_REG_MIPS_VEC_* and KVM_REG_MIPS_MSA_* registers can be
accessed, and the Config5.MSAEn bit is accessible via the KVM API and also from
the guest.
+6.74 KVM_CAP_SYNC_REGS
+Architectures: s390, x86 (vmx-only)
+Target: s390: always enabled, x86: vcpu
+Parameters: s390: none, x86: args[0] takes bitmask selecting which register
+sets to copy out (bitfields defined in arch/x86/include/uapi/asm/kvm.h).
+
+As described above in the kvm_sync_regs struct info in section 5 (kvm_run):
+KVM_CAP_SYNC_REGS "allow[s] userspace to access certain guest registers
+without having to call SET/GET_*REGS". This reduces overhead by eliminating
+repeated ioctl calls for setting and/or getting register values. This is
+particularly important when userspace is making synchronous guest state
+modifications, e.g. when emulating and/or intercepting instructions in
+userspace.
+
+For s390 specifics, please the source code.
+
+For x86:
+- the capability can be enabled/disabled (s390 is always enabled).
+- the register sets to be copied out out to kvm_run are selectable
+ by userspace (rather that all sets being copied out for every exit).
+- vcpu_events and selectable MSRs are available in addition to the
+ basic register sets (regs, sregs, debug_regs, and fpu).
+
+In addition to the register sets, the x86 'kvm_sync_regs' struct definition
+includes the bitarray, 'sync_regs', that toggles whether specific register
+sets are to be copied out. When enabling SYNC_REGS via KVM_CAP_ENABLE, the
+value in args[0] is copied into the 'sync_regs' bitarray value by KVM. But
+like the register sets, the copy-out field can be modified while handling
+an exit so that additonal KVM_CAP_ENABLE ioctl calls can be avoided.
+
+To indicate when userspace has modified values that should be copied into
+the vCPU, the all architecture bitarray field, 'kvm_dirty_regs' must be set.
+This is done using the same bitflags as for the 'sync_regs' copy-out field.
+If the dirty bit is not set, then the register values will not be copied
+into the vCPU even if they've been modified.
+
+Unused bitfields in the bitarrays must be set to zero.
+
+struct kvm_sync_regs {
+ __u64 sync_regs;
+ struct kvm_regs regs;
+ struct kvm_sregs sregs;
+ struct kvm_debugregs debugregs;
+ struct kvm_fpu fpu;
+ struct kvm_vcpu_events events;
+ struct kvm_msrs msrs;
+ struct kvm_msr_entry msr_entries[SYNC_REGS_NUM_MSRS];
+};
+
7. Capabilities that can be enabled on VMs
------------------------------------------
diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index c2824d02ba37..cdee17a4b0ee 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -353,8 +353,38 @@ struct kvm_xcrs {
__u64 padding[16];
};
-/* definition of registers in kvm_run */
+#define KVM_SYNC_X86_REGS (1UL << 0)
+#define KVM_SYNC_X86_SREGS (1UL << 1)
+#define KVM_SYNC_X86_DEBUGREGS (1UL << 2)
+#define KVM_SYNC_X86_FPU (1UL << 3)
+#define KVM_SYNC_X86_EVENTS (1UL << 4)
+#define KVM_SYNC_X86_MSRS (1UL << 5)
+#define KVM_SYNC_X86_NUM_FIELDS 6
+
+#define KVM_SYNC_X86_VALID_BITS \
+ (KVM_SYNC_X86_REGS| \
+ KVM_SYNC_X86_SREGS| \
+ KVM_SYNC_X86_DEBUGREGS| \
+ KVM_SYNC_X86_FPU| \
+ KVM_SYNC_X86_EVENTS| \
+ KVM_SYNC_X86_MSRS)
+
+#define SYNC_REGS_NUM_MSRS 8
+/* kvm_sync_regs struct included by kvm_run struct */
struct kvm_sync_regs {
+ /* Members of this structure are potentially malicious.
+ * Care must be taken by code reading, esp. interpreting,
+ * data fields from them inside KVM to prevent TOCTOU and
+ * double-fetch types of vulnerabilities.
+ */
+ __u64 sync_regs;
+ struct kvm_regs regs;
+ struct kvm_sregs sregs;
+ struct kvm_debugregs debugregs;
+ struct kvm_fpu fpu;
+ struct kvm_vcpu_events events;
+ struct kvm_msrs msrs;
+ struct kvm_msr_entry msr_entries[SYNC_REGS_NUM_MSRS];
};
#define KVM_X86_QUIRK_LINT0_REENABLED (1 << 0)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cd17b7d9a107..ad3f84cbf7f3 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -100,6 +100,8 @@ static void update_cr8_intercept(struct kvm_vcpu *vcpu);
static void process_nmi(struct kvm_vcpu *vcpu);
static void enter_smm(struct kvm_vcpu *vcpu);
static void __kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags);
+static void sync_regs_store_to_kvmrun(struct kvm_vcpu *vcpu);
+static int sync_regs_load_from_kvmrun(struct kvm_vcpu *vcpu);
struct kvm_x86_ops *kvm_x86_ops __read_mostly;
EXPORT_SYMBOL_GPL(kvm_x86_ops);
@@ -2587,15 +2589,22 @@ EXPORT_SYMBOL_GPL(kvm_get_msr_common);
*
* @return number of msrs set successfully.
*/
-static int __msr_io(struct kvm_vcpu *vcpu, struct kvm_msrs *msrs,
+static int __msr_io(struct kvm_vcpu *vcpu, u32 nmsrs, struct kvm_msrs *msrs,
struct kvm_msr_entry *entries,
int (*do_msr)(struct kvm_vcpu *vcpu,
unsigned index, u64 *data))
{
int i, idx;
+ /* For SYNC_REGS call into __msr_io, it is possible that userspace
+ * might have modified the count since it was snapshotted. Could be
+ * accidental but might be intentional attempt at TOCTOU.
+ */
+ if (nmsrs != msrs->nmsrs)
+ return -EINVAL;
+
idx = srcu_read_lock(&vcpu->kvm->srcu);
- for (i = 0; i < msrs->nmsrs; ++i)
+ for (i = 0; i < nmsrs; ++i)
if (do_msr(vcpu, entries[i].index, &entries[i].data))
break;
srcu_read_unlock(&vcpu->kvm->srcu, idx);
@@ -2633,7 +2642,7 @@ static int msr_io(struct kvm_vcpu *vcpu, struct kvm_msrs __user *user_msrs,
goto out;
}
- r = n = __msr_io(vcpu, &msrs, entries, do_msr);
+ r = n = __msr_io(vcpu, msrs.nmsrs, &msrs, entries, do_msr);
if (r < 0)
goto out_free;
@@ -2665,6 +2674,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_NOP_IO_DELAY:
case KVM_CAP_MP_STATE:
case KVM_CAP_SYNC_MMU:
+ case KVM_CAP_SYNC_REGS:
case KVM_CAP_USER_NMI:
case KVM_CAP_REINJECT_CONTROL:
case KVM_CAP_IRQ_INJECT_STATUS:
@@ -3435,6 +3445,11 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
return -EINVAL;
return kvm_hv_activate_synic(vcpu, cap->cap ==
KVM_CAP_HYPERV_SYNIC2);
+ case KVM_CAP_SYNC_REGS:
+ if (cap->args[0] & ~KVM_SYNC_X86_VALID_BITS)
+ return -EINVAL;
+ vcpu->run->s.regs.sync_regs = cap->args[0];
+ return 0;
default:
return -EINVAL;
}
@@ -7247,6 +7262,12 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
goto out;
}
+ if (vcpu->run->kvm_dirty_regs) {
+ r = sync_regs_load_from_kvmrun(vcpu);
+ if (r != 0)
+ goto out;
+ }
+
/* re-sync apic's tpr */
if (!lapic_in_kernel(vcpu)) {
if (kvm_set_cr8(vcpu, kvm_run->cr8) != 0) {
@@ -7270,6 +7291,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
r = vcpu_run(vcpu);
out:
+ if (vcpu->run->s.regs.sync_regs)
+ sync_regs_store_to_kvmrun(vcpu);
post_kvm_run_save(vcpu);
if (vcpu->sigset_active)
sigprocmask(SIG_SETMASK, &sigsaved, NULL);
@@ -7648,6 +7671,111 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
return 0;
}
+static void sync_regs_store_to_kvmrun(struct kvm_vcpu *vcpu)
+{
+ BUILD_BUG_ON(sizeof(struct kvm_sync_regs) > SYNC_REGS_UNION_SIZE_BYTES);
+ vcpu->run->kvm_valid_regs = 0;
+
+ if (vcpu->run->s.regs.sync_regs & KVM_SYNC_X86_REGS) {
+ kvm_arch_vcpu_ioctl_get_regs(vcpu, &vcpu->run->s.regs.regs);
+ vcpu->run->kvm_valid_regs |= KVM_SYNC_X86_REGS;
+ }
+ if (vcpu->run->s.regs.sync_regs & KVM_SYNC_X86_SREGS) {
+ kvm_arch_vcpu_ioctl_get_sregs(vcpu, &vcpu->run->s.regs.sregs);
+ vcpu->run->kvm_valid_regs |= KVM_SYNC_X86_SREGS;
+ }
+ if (vcpu->run->s.regs.sync_regs & KVM_SYNC_X86_DEBUGREGS) {
+ kvm_vcpu_ioctl_x86_get_debugregs(
+ vcpu, &vcpu->run->s.regs.debugregs);
+ vcpu->run->kvm_valid_regs |= KVM_SYNC_X86_DEBUGREGS;
+ }
+ if (vcpu->run->s.regs.sync_regs & KVM_SYNC_X86_FPU) {
+ kvm_arch_vcpu_ioctl_get_fpu(vcpu, &vcpu->run->s.regs.fpu);
+ vcpu->run->kvm_valid_regs |= KVM_SYNC_X86_FPU;
+ }
+ if (vcpu->run->s.regs.sync_regs & KVM_SYNC_X86_EVENTS) {
+ kvm_vcpu_ioctl_x86_get_vcpu_events(
+ vcpu, &vcpu->run->s.regs.events);
+ vcpu->run->kvm_valid_regs |= KVM_SYNC_X86_EVENTS;
+ }
+ if (vcpu->run->s.regs.sync_regs & KVM_SYNC_X86_MSRS) {
+ u32 nmsrs = vcpu->run->s.regs.msrs.nmsrs;
+
+ if (nmsrs > SYNC_REGS_NUM_MSRS)
+ nmsrs = vcpu->run->s.regs.msrs.nmsrs
+ = SYNC_REGS_NUM_MSRS;
+ __msr_io(vcpu, nmsrs, &vcpu->run->s.regs.msrs,
+ vcpu->run->s.regs.msr_entries, do_get_msr);
+ vcpu->run->kvm_valid_regs |= KVM_SYNC_X86_MSRS;
+ }
+}
+
+static int sync_regs_load_from_kvmrun(struct kvm_vcpu *vcpu)
+{
+ int r = -EINVAL;
+
+ if (unlikely(vcpu->run->kvm_dirty_regs == 0))
+ goto out;
+
+ if (vcpu->run->kvm_dirty_regs & ~KVM_SYNC_X86_VALID_BITS)
+ goto out;
+
+ if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_REGS) {
+ if (kvm_arch_vcpu_ioctl_set_regs(
+ vcpu, &vcpu->run->s.regs.regs))
+ goto out;
+ vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_REGS;
+ }
+ if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_SREGS) {
+ if (kvm_arch_vcpu_ioctl_set_sregs(
+ vcpu, &vcpu->run->s.regs.sregs))
+ goto out;
+ vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_SREGS;
+ }
+ if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_DEBUGREGS) {
+ if (kvm_vcpu_ioctl_x86_set_debugregs(
+ vcpu, &vcpu->run->s.regs.debugregs))
+ goto out;
+ vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_DEBUGREGS;
+ }
+ if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_FPU) {
+ if (kvm_arch_vcpu_ioctl_set_fpu(
+ vcpu, &vcpu->run->s.regs.fpu))
+ goto out;
+ vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_FPU;
+ }
+ if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_EVENTS) {
+ if (kvm_vcpu_ioctl_x86_set_vcpu_events(
+ vcpu, &vcpu->run->s.regs.events))
+ goto out;
+ vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_EVENTS;
+ }
+ if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_MSRS) {
+ u32 nmsrs_in = vcpu->run->s.regs.msrs.nmsrs;
+ u32 nmsrs_out = 0;
+
+ if (!nmsrs_in)
+ goto out;
+ else if (nmsrs_in > SYNC_REGS_NUM_MSRS) {
+ r = -E2BIG;
+ goto out;
+ }
+ nmsrs_out = __msr_io(vcpu, nmsrs_in, &vcpu->run->s.regs.msrs,
+ vcpu->run->s.regs.msr_entries, do_set_msr);
+ if (!nmsrs_out) {
+ r = -EINVAL;
+ goto out;
+ } else if (nmsrs_in != nmsrs_out) {
+ r = nmsrs_out;
+ goto out;
+ }
+ vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_MSRS;
+ }
+ r = 0;
+out:
+ return r;
+}
+
static void fx_init(struct kvm_vcpu *vcpu)
{
fpstate_init(&vcpu->arch.guest_fpu.state);
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 838887587411..90a6b24df901 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -395,6 +395,10 @@ struct kvm_run {
char padding[256];
};
+ /* 2048 is the size of the char array IBM used to bound/pad the size
+ * of the union that holds sync regs.
+ */
+#define SYNC_REGS_UNION_SIZE_BYTES 2048
/*
* shared registers between kvm and userspace.
* kvm_valid_regs specifies the register classes set by the host
@@ -406,7 +410,7 @@ struct kvm_run {
__u64 kvm_dirty_regs;
union {
struct kvm_sync_regs regs;
- char padding[2048];
+ char padding[SYNC_REGS_UNION_SIZE_BYTES];
} s;
};
--
2.14.1.690.gbb1197296e-goog
