linux-kernel - [RFC PATCH 8/8] x86/fpu/xstate: WARN if normal fpstate contains kernel dynamic xfeatures

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Date:   Wed, 13 Sep 2023 23:23:34 -0400
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     dave.hansen@...el.com, tglx@...utronix.de, peterz@...radead.org,
        seanjc@...gle.com, pbonzini@...hat.com, rick.p.edgecombe@...el.com,
        kvm@...r.kernel.org, yang.zhong@...el.com, jing2.liu@...el.com,
        chao.gao@...el.com, Yang Weijiang <weijiang.yang@...el.com>
Subject: [RFC PATCH 8/8] x86/fpu/xstate: WARN if normal fpstate contains kernel dynamic xfeatures

fpu_kernel_dynamic_xfeatures now are __ONLY__ enabled by guest kernel and
used for guest fpstate, i.e., none for normal fpstate. The bits are added
when guest fpstate is allocated and fpstate->is_guest set to %true.

For normal fpstate, the bits should have been removed when init system FPU
settings, WARN_ONCE() if normal fpstate contains kernel dynamic xfeatures
before xsaves is executed.

Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
---
 arch/x86/kernel/fpu/xstate.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index 9c6e3ca05c5c..c2b33a5db53d 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -186,6 +186,9 @@ static inline void os_xsave(struct fpstate *fpstate)
 	WARN_ON_FPU(!alternatives_patched);
 	xfd_validate_state(fpstate, mask, false);
 
+	WARN_ON_FPU(!fpstate->is_guest &&
+		    (mask & fpu_kernel_dynamic_xfeatures));
+
 	XSTATE_XSAVE(&fpstate->regs.xsave, lmask, hmask, err);
 
 	/* We should never fault when copying to a kernel buffer: */
-- 
2.27.0