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x86: Grant AMX permission for guest

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Kernel allocates 4K xstate buffer by default. For XSAVE features
which require large state component (e.g. AMX), Linux kernel
dynamically expands the xstate buffer only after the process has
acquired the necessary permissions. Those are called dynamically-
enabled XSAVE features (or dynamic xfeatures).

There are separate permissions for native tasks and guests.

Qemu should request the guest permissions for dynamic xfeatures
which will be exposed to the guest. This only needs to be done
once before the first vcpu is created.

KVM implemented one new ARCH_GET_XCOMP_SUPP system attribute API to
get host side supported_xcr0 and Qemu can decide if it can request
dynamically enabled XSAVE features permission.
https://lore.kernel.org/all/20220126152210.3044876-1-pbonzini@redhat.com/

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Message-Id: <20220217060434.52460-4-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Yang Zhong 2022-02-16 22:04:29 -08:00 • committed by Paolo Bonzini
parent 1f16764f7d
commit 19db68ca68
5 changed files with 75 additions and 6 deletions
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target/i386/kvm/kvm_i386.h
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@ -52,5 +52,6 @@ bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp);
uint64_t kvm_swizzle_msi_ext_dest_id(uint64_t address);
bool kvm_enable_sgx_provisioning(KVMState *s);
void kvm_request_xsave_components(X86CPU *cpu, uint64_t mask);
#endif