linux-kernel - [PATCH 5.15 04/20] KVM: Fix steal time asm constraints

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Message-Id: <20211119171444.786349477@linuxfoundation.org>
Date:   Fri, 19 Nov 2021 18:39:22 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, kernel test robot <lkp@...el.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.15 04/20] KVM: Fix steal time asm constraints

From: David Woodhouse <dwmw@...zon.co.uk>

commit 964b7aa0b040bdc6ec1c543ee620cda3f8b4c68a upstream.

In 64-bit mode, x86 instruction encoding allows us to use the low 8 bits
of any GPR as an 8-bit operand. In 32-bit mode, however, we can only use
the [abcd] registers. For which, GCC has the "q" constraint instead of
the less restrictive "r".

Also fix st->preempted, which is an input/output operand rather than an
input.

Fixes: 7e2175ebd695 ("KVM: x86: Fix recording of guest steal time / preempted status")
Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
Message-Id: <89bf72db1b859990355f9c40713a34e0d2d86c98.camel@...radead.org>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kvm/x86.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3242,9 +3242,9 @@ static void record_steal_time(struct kvm
 			     "xor %1, %1\n"
 			     "2:\n"
 			     _ASM_EXTABLE_UA(1b, 2b)
-			     : "+r" (st_preempted),
-			       "+&r" (err)
-			     : "m" (st->preempted));
+			     : "+q" (st_preempted),
+			       "+&r" (err),
+			       "+m" (st->preempted));
 		if (err)
 			goto out;