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kvm: x86: Add support for getting/setting expanded xstate buffer

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With KVM_CAP_XSAVE, userspace uses a hardcoded 4KB buffer to get/set
xstate data from/to KVM. This doesn't work when dynamic xfeatures
(e.g. AMX) are exposed to the guest as they require a larger buffer
size.

Introduce a new capability (KVM_CAP_XSAVE2). Userspace VMM gets the
required xstate buffer size via KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2).
KVM_SET_XSAVE is extended to work with both legacy and new capabilities
by doing properly-sized memdup_user() based on the guest fpu container.
KVM_GET_XSAVE is kept for backward-compatible reason. Instead,
KVM_GET_XSAVE2 is introduced under KVM_CAP_XSAVE2 as the preferred
interface for getting xstate buffer (4KB or larger size) from KVM
(Link: https://lkml.org/lkml/2021/12/15/510)

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>
Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Message-Id: <20220105123532.12586-19-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Guang Zeng
2022-01-05 04:35:29 -08:00
committed by Paolo Bonzini
parent c60427dd50
commit be50b2065d
6 changed files with 106 additions and 5 deletions
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16
arch/x86/include/uapi/asm/kvm.h
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@@ -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