[PATCH -hyperv 1/3] x86/hyperv: Save segment registers directly to memory in hv_hvcrash_ctxt_save()

Uros Bizjak
2026-03-11T10:27:22Z

hv_hvcrash_ctxt_save() in arch/x86/hyperv/hv_crash.c currently saves
segment registers via a general-purpose register (%eax). Update the
code to save segment registers (cs, ss, ds, es, fs, gs) directly to
the crash context memory using movw. This avoids unnecessary use of
a general-purpose register, making the code simpler and more efficient.

The size of the corresponding object file improves as follows:

text data bss dec hex filename
4167 176 200 4543 11bf hv_crash-old.o
4151 176 200 4527 11af hv_crash-new.o

No functional change occurs to the saved context contents; this is
purely a code-quality improvement.

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 | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/x86/hyperv/hv_crash.c b/arch/x86/hyperv/hv_crash.c
index fdb277bf73d8..2c7ea7e70854 100644
--- a/arch/x86/hyperv/hv_crash.c
+++ b/arch/x86/hyperv/hv_crash.c
@@ -207,12 +207,12 @@ static void hv_hvcrash_ctxt_save(void)
asm volatile("movq %%cr2, %0" : "=a"(ctxt->cr2));
asm volatile("movq %%cr8, %0" : "=a"(ctxt->cr8));

- asm volatile("movl %%cs, %%eax" : "=a"(ctxt->cs));
- asm volatile("movl %%ss, %%eax" : "=a"(ctxt->ss));
- asm volatile("movl %%ds, %%eax" : "=a"(ctxt->ds));
- asm volatile("movl %%es, %%eax" : "=a"(ctxt->es));
- asm volatile("movl %%fs, %%eax" : "=a"(ctxt->fs));
- asm volatile("movl %%gs, %%eax" : "=a"(ctxt->gs));
+ asm volatile("movw %%cs, %0" : "=m"(ctxt->cs));
+ asm volatile("movw %%ss, %0" : "=m"(ctxt->ss));
+ asm volatile("movw %%ds, %0" : "=m"(ctxt->ds));
+ asm volatile("movw %%es, %0" : "=m"(ctxt->es));
+ asm volatile("movw %%fs, %0" : "=m"(ctxt->fs));
+ asm volatile("movw %%gs, %0" : "=m"(ctxt->gs));

native_store_gdt(&ctxt->gdtr);
store_idt(&ctxt->idtr);
--
2.53.0