linux-kernel - [kvm-unit-tests PATCH v2 4/4] arm: fpu: Fix the input/output args for inline asm in fpu.c

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Message-ID: <20241023152638.3317648-5-rananta@google.com>
Date: Wed, 23 Oct 2024 15:26:38 +0000
From: Raghavendra Rao Ananta <rananta@...gle.com>
To: Subhasish Ghosh <subhasish.ghosh@....com>, Joey Gouly <joey.gouly@....com>, 
	Andrew Jones <andrew.jones@...ux.dev>
Cc: Oliver Upton <oliver.upton@...ux.dev>, Marc Zyngier <maz@...nel.org>, 
	Raghavendra Rao Anata <rananta@...gle.com>, linux-arm-kernel@...ts.infradead.org, 
	kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: [kvm-unit-tests PATCH v2 4/4] arm: fpu: Fix the input/output args for
 inline asm in fpu.c

The macros fpu_reg_{read,write} post-increment the '__val'
pointer register as a part of 'stp' and 'ldp' instructions.
As a result, mark it with "+r" for the compiler to treat it
as read-write operand.

On the contrary, sve_reg_read() never updates the value of the
pointer/register. Hence, mark this as "r" for the compiler to
treat it as read-only operand.

Without these adjustments, the compiler can potentially perform
optimizations over the registers holding the pointers that could
lead to data aborts.

Fixes: d47d370c8f ("arm: Add test for FPU/SIMD context save/restore")
Signed-off-by: Raghavendra Rao Ananta <rananta@...gle.com>
---
 arm/fpu.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arm/fpu.c b/arm/fpu.c
index f327a349..f44ed82a 100644
--- a/arm/fpu.c
+++ b/arm/fpu.c
@@ -55,7 +55,7 @@ static inline bool arch_collect_entropy(uint64_t *random)
 		     "stp q26, q27, [%0], #32\n\t"	\
 		     "stp q28, q29, [%0], #32\n\t"	\
 		     "stp q30, q31, [%0], #32\n\t"	\
-		     : "=r" (__val)			\
+		     : "+r" (__val)			\
 		     :					\
 		     : "v0", "v1", "v2", "v3",		\
 			"v4", "v5", "v6", "v7",		\
@@ -89,8 +89,8 @@ do {							\
 		     "ldp q26, q27, [%0], #32\n\t"	\
 		     "ldp q28, q29, [%0], #32\n\t"	\
 		     "ldp q30, q31, [%0], #32\n\t"	\
+		     : "+r" (__val)			\
 		     :					\
-		     : "r" (__val)			\
 		     : "v0", "v1", "v2", "v3",		\
 			"v4", "v5", "v6", "v7",		\
 			"v8", "v9", "v10", "v11",	\
@@ -140,8 +140,8 @@ do {							\
 		     "str z29, [%0, #29, MUL VL]\n"	\
 		     "str z30, [%0, #30, MUL VL]\n"	\
 		     "str z31, [%0, #31, MUL VL]\n"	\
-		     : "=r" (__val)			\
 		     :					\
+		     : "r" (__val)			\
 		     : "z0", "z1", "z2", "z3",		\
 			"z4", "z5", "z6", "z7",		\
 			"z8", "z9", "z10", "z11",	\
-- 
2.47.0.105.g07ac214952-goog