Define a new XFEATURE_MASK_KERNEL_DYNAMIC mask to specify the features that can be optionally enabled by kernel components. This is similar to XFEATURE_MASK_USER_DYNAMIC in that it contains optional xfeatures that can allows the FPU buffer to be dynamically sized. The difference is that the KERNEL variant contains supervisor features and will be enabled by kernel components that need them, and not directly by the user. Currently it's used by KVM to configure guest dedicated fpstate for calculating the xfeature and fpstate storage size etc. The kernel dynamic xfeatures now only contain XFEATURE_CET_KERNEL, which is supported by host as they're enabled in kernel XSS MSR setting but relevant CPU feature, i.e., supervisor shadow stack, is not enabled in host kernel therefore it can be omitted for normal fpstate by default. Remove the kernel dynamic feature from fpu_kernel_cfg.default_features so that the bits in xstate_bv and xcomp_bv are cleared and xsaves/xrstors can be optimized by HW for normal fpstate. Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxx> Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx> Reviewed-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> --- arch/x86/include/asm/fpu/xstate.h | 5 ++++- arch/x86/kernel/fpu/xstate.c | 1 + 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h index 3b4a038d3c57..a212d3851429 100644 --- a/arch/x86/include/asm/fpu/xstate.h +++ b/arch/x86/include/asm/fpu/xstate.h @@ -46,9 +46,12 @@ #define XFEATURE_MASK_USER_RESTORE \ (XFEATURE_MASK_USER_SUPPORTED & ~XFEATURE_MASK_PKRU) -/* Features which are dynamically enabled for a process on request */ +/* Features which are dynamically enabled per userspace request */ #define XFEATURE_MASK_USER_DYNAMIC XFEATURE_MASK_XTILE_DATA +/* Features which are dynamically enabled per kernel side request */ +#define XFEATURE_MASK_KERNEL_DYNAMIC XFEATURE_MASK_CET_KERNEL + /* All currently supported supervisor features */ #define XFEATURE_MASK_SUPERVISOR_SUPPORTED (XFEATURE_MASK_PASID | \ XFEATURE_MASK_CET_USER | \ diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index 03e166a87d61..ca4b83c142eb 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -824,6 +824,7 @@ void __init fpu__init_system_xstate(unsigned int legacy_size) /* Clean out dynamic features from default */ fpu_kernel_cfg.default_features = fpu_kernel_cfg.max_features; fpu_kernel_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC; + fpu_kernel_cfg.default_features &= ~XFEATURE_MASK_KERNEL_DYNAMIC; fpu_user_cfg.default_features = fpu_user_cfg.max_features; fpu_user_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC; -- 2.43.0
