[PATCH v3 03/10] x86/fpu/xstate: Correct xfeatures cache in guest pseudo fpu container

Chao Gao
2025-03-07T16:39:03Z

The xfeatures field in struct fpu_guest is designed to track the enabled
xfeatures for guest FPUs. However, during allocation in
fpu_alloc_guest_fpstate(), gfpu->xfeatures is initialized to
fpu_user_cfg.default_features, while the corresponding
fpstate->xfeatures is set to fpu_kernel_cfg.default_features

Correct the mismatch to avoid confusion.

Note this mismatch does not cause any functional issues. The
gfpu->xfeatures is checked in fpu_enable_guest_xfd_features() to
verify if XFD features are already enabled:

xfeatures &= ~guest_fpu->xfeatures;
if (!xfeatures)
return 0;

It gets updated in fpstate_realloc() after enabling some XFD features:

guest_fpu->xfeatures |= xfeatures;

So, backport is not needed.

Signed-off-by: Chao Gao <chao.gao@intel.com>
---
arch/x86/kernel/fpu/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index dc169f3d336d..6166a928d3f5 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -230,7 +230,7 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
fpstate->is_guest = true;

gfpu->fpstate = fpstate;
- gfpu->xfeatures = fpu_user_cfg.default_features;
+ gfpu->xfeatures = fpu_kernel_cfg.default_features;

/*
* KVM sets the FP+SSE bits in the XSAVE header when copying FPU state
--
2.46.1