linux-kernel - [PATCH RFC v1 03/11] x86/fpu/xstate: Remove xstate offset check

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Message-ID: <20250227184502.10288-4-chang.seok.bae@intel.com>
Date: Thu, 27 Feb 2025 10:44:48 -0800
From: "Chang S. Bae" <chang.seok.bae@...el.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	chang.seok.bae@...el.com
Subject: [PATCH RFC v1 03/11] x86/fpu/xstate: Remove xstate offset check

Traditionally, new xstate components have been assigned sequentially,
aligning feature numbers with their offsets in the XSAVE buffer. However,
this ordering is not architecturally mandated in the non-compacted
format, where a component's offset may not correspond to its feature
number.

The kernel caches CPUID-reported xstate component details, including size
and offset in the non-compacted format. As part of this process, a sanity
check is also conducted to ensure alignment between feature numbers and
offsets.

This check was likely intended as a general guideline rather than a
strict requirement. As part of supporting out-of-order offsets, remove
this unnecessary validation.

Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
---
 arch/x86/kernel/fpu/xstate.c | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index cee9a1e454b7..c6f825bb744b 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -253,9 +253,6 @@ static bool xfeature_enabled(enum xfeature xfeature)
 static void __init setup_xstate_cache(void)
 {
 	u32 eax, ebx, ecx, edx, i;
-	/* start at the beginning of the "extended state" */
-	unsigned int last_good_offset = offsetof(struct xregs_state,
-						 extended_state_area);
 	/*
 	 * The FP xstates and SSE xstates are legacy states. They are always
 	 * in the fixed offsets in the xsave area in either compacted form
@@ -283,16 +280,6 @@ static void __init setup_xstate_cache(void)
 			continue;
 
 		xstate_offsets[i] = ebx;
-
-		/*
-		 * In our xstate size checks, we assume that the highest-numbered
-		 * xstate feature has the highest offset in the buffer.  Ensure
-		 * it does.
-		 */
-		WARN_ONCE(last_good_offset > xstate_offsets[i],
-			  "x86/fpu: misordered xstate at %d\n", last_good_offset);
-
-		last_good_offset = xstate_offsets[i];
 	}
 }
 
-- 
2.45.2