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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>
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