tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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x86/hyperv: Save segment registers directly to memory in hv_hvcrash_ctxt_save()

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>
Signed-off-by: Wei Liu <wei.liu@kernel.org>

authored by

Uros Bizjak and committed by
Wei Liu 3484127c 3fde5281

+6 -6
+6 -6
arch/x86/hyperv/hv_crash.c
··· 207 207 asm volatile("movq %%cr2, %0" : "=a"(ctxt->cr2)); 208 208 asm volatile("movq %%cr8, %0" : "=a"(ctxt->cr8)); 209 209 210 - asm volatile("movl %%cs, %%eax" : "=a"(ctxt->cs)); 211 - asm volatile("movl %%ss, %%eax" : "=a"(ctxt->ss)); 212 - asm volatile("movl %%ds, %%eax" : "=a"(ctxt->ds)); 213 - asm volatile("movl %%es, %%eax" : "=a"(ctxt->es)); 214 - asm volatile("movl %%fs, %%eax" : "=a"(ctxt->fs)); 215 - asm volatile("movl %%gs, %%eax" : "=a"(ctxt->gs)); 210 + asm volatile("movw %%cs, %0" : "=m"(ctxt->cs)); 211 + asm volatile("movw %%ss, %0" : "=m"(ctxt->ss)); 212 + asm volatile("movw %%ds, %0" : "=m"(ctxt->ds)); 213 + asm volatile("movw %%es, %0" : "=m"(ctxt->es)); 214 + asm volatile("movw %%fs, %0" : "=m"(ctxt->fs)); 215 + asm volatile("movw %%gs, %0" : "=m"(ctxt->gs)); 216 216 217 217 native_store_gdt(&ctxt->gdtr); 218 218 store_idt(&ctxt->idtr);