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

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Message-ID: <20250307164123.1613414-4-chao.gao@intel.com>
Date: Sat,  8 Mar 2025 00:41:16 +0800
From: Chao Gao <chao.gao@...el.com>
To: chao.gao@...el.com,
	tglx@...utronix.de,
	dave.hansen@...el.com,
	x86@...nel.org,
	seanjc@...gle.com,
	pbonzini@...hat.com,
	linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc: peterz@...radead.org,
	rick.p.edgecombe@...el.com,
	weijiang.yang@...el.com,
	john.allen@....com,
	bp@...en8.de
Subject: [PATCH v3 03/10] x86/fpu/xstate: Correct xfeatures cache in guest pseudo fpu container

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@...el.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