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Subject[PATCH v3 19/22] kvm: x86: Get/set expanded xstate buffer
Date
From: Guang Zeng <guang.zeng@intel.com>

When AMX is enabled it requires a larger xstate buffer than
the legacy hardcoded 4KB one. Exising kvm ioctls
(KVM_[G|S]ET_XSAVE under KVM_CAP_XSAVE) are not suitable for
this purpose.

A new capability (KVM_CAP_XSAVE2) is introduced to mark an
extended kvm_xsave format to support >4KB fpstate. The expanded
fpstate size is returned to userspace when it checks the
KVM_CAP_XSAVE2 capability.

Introduce a new KVM_GET_XSAVE2 under this capability to use the
new format for copying guest fpstate to userspace. Reuse
KVM_SET_XSAVE for both old/new formats by reimplementing it to
do properly-sized memdup_user() based on the guest fpu container.

Also, update the api doc with the new KVM_GET_XSAVE2 ioctl.

Signed-off-by: Guang Zeng <guang.zeng@intel.com>
Signed-off-by: Wei Wang <wei.w.wang@intel.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
---
Documentation/virt/kvm/api.rst | 42 +++++++++++++++++++++++++++++++--
arch/x86/include/uapi/asm/kvm.h | 16 ++++++++++++-
arch/x86/kvm/x86.c | 39 +++++++++++++++++++++++++++++-
include/uapi/linux/kvm.h | 4 ++++
4 files changed, 97 insertions(+), 4 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 1cf2483246cd..e48f7de5f23a 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -1566,6 +1566,7 @@ otherwise it will return EBUSY error.

struct kvm_xsave {
__u32 region[1024];
+ __u32 extra[0];
};

This ioctl would copy current vcpu's xsave struct to the userspace.
@@ -1574,7 +1575,7 @@ This ioctl would copy current vcpu's xsave struct to the userspace.
4.43 KVM_SET_XSAVE
------------------

-:Capability: KVM_CAP_XSAVE
+:Capability: KVM_CAP_XSAVE and KVM_CAP_XSAVE2
:Architectures: x86
:Type: vcpu ioctl
:Parameters: struct kvm_xsave (in)
@@ -1585,9 +1586,18 @@ This ioctl would copy current vcpu's xsave struct to the userspace.

struct kvm_xsave {
__u32 region[1024];
+ __u32 extra[0];
};

-This ioctl would copy userspace's xsave struct to the kernel.
+This ioctl would copy userspace's xsave struct to the kernel. It copies
+as many bytes as are returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2),
+when invoked on the vm file descriptor. The size value returned by
+KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) will always be at least 4096.
+Currently, it is only greater than 4096 if a dynamic feature has been
+enabled with ``arch_prctl()``, but this may change in the future.
+
+The offsets of the state save areas in struct kvm_xsave follow the
+contents of CPUID leaf 0xD on the host.


4.44 KVM_GET_XCRS
@@ -5507,6 +5517,34 @@ the trailing ``'\0'``, is indicated by ``name_size`` in the header.
The Stats Data block contains an array of 64-bit values in the same order
as the descriptors in Descriptors block.

+4.42 KVM_GET_XSAVE2
+------------------
+
+:Capability: KVM_CAP_XSAVE2
+:Architectures: x86
+:Type: vcpu ioctl
+:Parameters: struct kvm_xsave (out)
+:Returns: 0 on success, -1 on error
+
+
+::
+
+ struct kvm_xsave {
+ __u32 region[1024];
+ __u32 extra[0];
+ };
+
+This ioctl would copy current vcpu's xsave struct to the userspace. It
+copies as many bytes as are returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2)
+when invoked on the vm file descriptor. The size value returned by
+KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) will always be at least 4096.
+Currently, it is only greater than 4096 if a dynamic feature has been
+enabled with ``arch_prctl()``, but this may change in the future.
+
+The offsets of the state save areas in struct kvm_xsave follow the contents
+of CPUID leaf 0xD on the host.
+
+
5. The kvm_run structure
========================

diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 5a776a08f78c..2da3316bb559 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -373,9 +373,23 @@ struct kvm_debugregs {
__u64 reserved[9];
};

-/* for KVM_CAP_XSAVE */
+/* for KVM_CAP_XSAVE and KVM_CAP_XSAVE2 */
struct kvm_xsave {
+ /*
+ * KVM_GET_XSAVE2 and KVM_SET_XSAVE write and read as many bytes
+ * as are returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2)
+ * respectively, when invoked on the vm file descriptor.
+ *
+ * The size value returned by KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2)
+ * will always be at least 4096. Currently, it is only greater
+ * than 4096 if a dynamic feature has been enabled with
+ * ``arch_prctl()``, but this may change in the future.
+ *
+ * The offsets of the state save areas in struct kvm_xsave follow
+ * the contents of CPUID leaf 0xD on the host.
+ */
__u32 region[1024];
+ __u32 extra[0];
};

#define KVM_MAX_XCRS 16
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c558c098979a..3b756ff13103 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4297,6 +4297,11 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
else
r = 0;
break;
+ case KVM_CAP_XSAVE2:
+ r = kvm->vcpus[0]->arch.guest_fpu.uabi_size;
+ if (r < sizeof(struct kvm_xsave))
+ r = sizeof(struct kvm_xsave);
+ break;
default:
break;
}
@@ -4900,6 +4905,16 @@ static void kvm_vcpu_ioctl_x86_get_xsave(struct kvm_vcpu *vcpu,
vcpu->arch.pkru);
}

+static void kvm_vcpu_ioctl_x86_get_xsave2(struct kvm_vcpu *vcpu,
+ u8 *state, unsigned int size)
+{
+ if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
+ return;
+
+ fpu_copy_guest_fpstate_to_uabi(&vcpu->arch.guest_fpu,
+ state, size, vcpu->arch.pkru);
+}
+
static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu,
struct kvm_xsave *guest_xsave)
{
@@ -5367,7 +5382,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
break;
}
case KVM_SET_XSAVE: {
- u.xsave = memdup_user(argp, sizeof(*u.xsave));
+ int size = vcpu->arch.guest_fpu.uabi_size;
+
+ u.xsave = memdup_user(argp, size);
if (IS_ERR(u.xsave)) {
r = PTR_ERR(u.xsave);
goto out_nofree;
@@ -5376,6 +5393,26 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
r = kvm_vcpu_ioctl_x86_set_xsave(vcpu, u.xsave);
break;
}
+
+ case KVM_GET_XSAVE2: {
+ int size = vcpu->arch.guest_fpu.uabi_size;
+
+ u.xsave = kzalloc(size, GFP_KERNEL_ACCOUNT);
+ if (!u.xsave) {
+ r = -ENOMEM;
+ break;
+ }
+
+ kvm_vcpu_ioctl_x86_get_xsave2(vcpu, u.buffer, size);
+
+ if (copy_to_user(argp, u.xsave, size)) {
+ r = -EFAULT;
+ break;
+ }
+ r = 0;
+ break;
+ }
+
case KVM_GET_XCRS: {
u.xcrs = kzalloc(sizeof(struct kvm_xcrs), GFP_KERNEL_ACCOUNT);
r = -ENOMEM;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 1daa45268de2..9d1c01669560 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1131,6 +1131,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
#define KVM_CAP_ARM_MTE 205
#define KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM 206
+#define KVM_CAP_XSAVE2 207

#ifdef KVM_CAP_IRQ_ROUTING

@@ -1610,6 +1611,9 @@ struct kvm_enc_region {
#define KVM_S390_NORMAL_RESET _IO(KVMIO, 0xc3)
#define KVM_S390_CLEAR_RESET _IO(KVMIO, 0xc4)

+/* Available with KVM_CAP_XSAVE2 */
+#define KVM_GET_XSAVE2 _IOR(KVMIO, 0xcf, struct kvm_xsave)
+
struct kvm_s390_pv_sec_parm {
__u64 origin;
__u64 length;
--
2.27.0
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