linux-kernel - [PATCH v4 5/8] x86/fpu: Initialize guest FPU permissions from guest defaults

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Message-ID: <20250318153316.1970147-6-chao.gao@intel.com>
Date: Tue, 18 Mar 2025 23:31:55 +0800
From: Chao Gao <chao.gao@...el.com>
To: x86@...nel.org,
	linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org,
	tglx@...utronix.de,
	dave.hansen@...el.com,
	seanjc@...gle.com,
	pbonzini@...hat.com
Cc: peterz@...radead.org,
	rick.p.edgecombe@...el.com,
	weijiang.yang@...el.com,
	john.allen@....com,
	bp@...en8.de,
	chang.seok.bae@...el.com,
	xin3.li@...el.com,
	Chao Gao <chao.gao@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Uros Bizjak <ubizjak@...il.com>,
	Eric Biggers <ebiggers@...gle.com>,
	Stanislav Spassov <stanspas@...zon.de>
Subject: [PATCH v4 5/8] x86/fpu: Initialize guest FPU permissions from guest defaults

Currently, fpu->guest_perm is copied from fpu->perm, which is derived from
fpu_kernel_cfg.default_features.

Initialize guest FPU permissions from guest defaults instead of host
defaults. This ensures that any changes to guest_default_{features,size}
are automatically reflected in guest permissions, which in turn guarantees
that fpstate_realloc() allocates a correctly sized XSAVE buffer for guest
FPUs.

Signed-off-by: Chao Gao <chao.gao@...el.com>
---
 arch/x86/kernel/fpu/core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 0b695c23bbfb..52df97a8a61b 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -542,8 +542,10 @@ void fpstate_reset(struct fpu *fpu)
 	fpu->perm.__state_perm		= fpu_kernel_cfg.default_features;
 	fpu->perm.__state_size		= fpu_kernel_cfg.default_size;
 	fpu->perm.__user_state_size	= fpu_user_cfg.default_size;
-	/* Same defaults for guests */
-	fpu->guest_perm = fpu->perm;
+
+	fpu->guest_perm.__state_perm	= fpu_kernel_cfg.guest_default_features;
+	fpu->guest_perm.__state_size	= fpu_kernel_cfg.guest_default_size;
+	fpu->guest_perm.__user_state_size = fpu_user_cfg.guest_default_size;
 }
 
 static inline void fpu_inherit_perms(struct fpu *dst_fpu)
-- 
2.46.1