From dda366083e5ff307a4a728757db874bbfe7550be Mon Sep 17 00:00:00 2001 From: Chao Gao Date: Mon, 17 Mar 2025 22:06:11 +0800 Subject: [PATCH] x86/fpu/xstate: Fix inconsistencies in guest FPU xfeatures Guest FPUs manage vCPU FPU states. They are allocated via fpu_alloc_guest_fpstate() and are resized in fpstate_realloc() when XFD features are enabled. Since the introduction of guest FPUs, there have been inconsistencies in the kernel buffer size and xfeatures: 1. fpu_alloc_guest_fpstate() uses fpu_user_cfg since its introduction. See: 69f6ed1d14c6 ("x86/fpu: Provide infrastructure for KVM FPU cleanup") 36487e6228c4 ("x86/fpu: Prepare guest FPU for dynamically enabled FPU features") 2. __fpstate_reset() references fpu_kernel_cfg to set storage attributes. 3. fpu->guest_perm uses fpu_kernel_cfg, affecting fpstate_realloc(). A recent commit in the tip:x86/fpu tree partially addressed the inconsistency between (1) and (3) by using fpu_kernel_cfg for size calculation in (1), but left fpu_guest->xfeatures and fpu_guest->perm still referencing fpu_user_cfg: https://lore.kernel.org/all/20250218141045.85201-1-stanspas@amazon.de/ 1937e18cc3cf ("x86/fpu: Fix guest FPU state buffer allocation size") The inconsistencies within fpu_alloc_guest_fpstate() and across the mentioned functions cause confusion. Fix them by using fpu_kernel_cfg consistently in fpu_alloc_guest_fpstate(), except for fields related to the UABI buffer. Referencing fpu_kernel_cfg won't impact functionalities, as: 1. fpu_guest->perm is overwritten shortly in fpu_init_guest_permissions() with fpstate->guest_perm, which already uses fpu_kernel_cfg. 2. fpu_guest->xfeatures is solely used to check if XFD features are enabled. Including supervisor xfeatures doesn't affect the check. Fixes: 36487e6228c4 ("x86/fpu: Prepare guest FPU for dynamically enabled FPU features") Suggested-by: Chang S. Bae Signed-off-by: Chao Gao Signed-off-by: Ingo Molnar Cc: Andy Lutomirski Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Dave Hansen Cc: Juergen Gross Cc: Stefano Stabellini Cc: Paolo Bonzini Cc: Vitaly Kuznetsov Cc: Sean Christopherson Cc: David Woodhouse Link: https://lore.kernel.org/r/20250317140613.1761633-1-chao.gao@intel.com --- arch/x86/kernel/fpu/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index 422c98ca6eb8..1b734a9ff088 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -239,8 +239,8 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu) fpstate->is_guest = true; gfpu->fpstate = fpstate; - gfpu->xfeatures = fpu_user_cfg.default_features; - gfpu->perm = fpu_user_cfg.default_features; + gfpu->xfeatures = fpu_kernel_cfg.default_features; + gfpu->perm = fpu_kernel_cfg.default_features; /* * KVM sets the FP+SSE bits in the XSAVE header when copying FPU state