[PATCH -hyperv 3/3] x86/hyperv: Use any general-purpose register when saving %cr2 and %cr8

Uros Bizjak
2026-03-11T10:27:28Z

hv_hvcrash_ctxt_save() in arch/x86/hyperv/hv_crash.c currently saves %cr2
and %cr8 using %eax ("=a"). This unnecessarily forces a specific register.
Update the inline assembly to use a general-purpose register ("=r") for
both %cr2 and %cr8. This makes the code more flexible for the compiler
while producing the same saved context contents.

No functional changes.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>
Cc: Dexuan Cui <decui@microsoft.com>
Cc: Long Li <longli@microsoft.com>
Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
---
arch/x86/hyperv/hv_crash.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/hyperv/hv_crash.c b/arch/x86/hyperv/hv_crash.c
index d0f95a278fdb..5ffcc23255de 100644
--- a/arch/x86/hyperv/hv_crash.c
+++ b/arch/x86/hyperv/hv_crash.c
@@ -204,8 +204,8 @@ static void hv_hvcrash_ctxt_save(void)
ctxt->cr0 = native_read_cr0();
ctxt->cr4 = native_read_cr4();

- asm volatile("movq %%cr2, %0" : "=a"(ctxt->cr2));
- asm volatile("movq %%cr8, %0" : "=a"(ctxt->cr8));
+ asm volatile("movq %%cr2, %0" : "=r"(ctxt->cr2));
+ asm volatile("movq %%cr8, %0" : "=r"(ctxt->cr8));

asm volatile("movw %%cs, %0" : "=m"(ctxt->cs));
asm volatile("movw %%ss, %0" : "=m"(ctxt->ss));
--
2.53.0