Messages in this thread | | | Date | Mon, 28 Nov 2022 11:03:20 +0800 | From | "Hou Wenlong" <> | Subject | Re: [PATCH v2] x86/paravirt: Use relative reference for original instruction |
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On Sun, Nov 27, 2022 at 09:24:34AM -0800, H. Peter Anvin wrote: > On November 24, 2022 3:51:53 AM PST, Hou Wenlong <houwenlong.hwl@antgroup.com> wrote: > >Similar to the alternative patching, use relative reference for original > >instruction rather than absolute one, which saves 8 bytes for one entry > >on x86_64. And it could generate R_X86_64_PC32 relocation instead of > >R_X86_64_64 relocation, which also reduces relocation metadata on > >relocatable builds. And the alignment could be hard coded to be 4 now. > > > >Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com> > >--- > > arch/x86/include/asm/paravirt.h | 10 +++++----- > > arch/x86/include/asm/paravirt_types.h | 8 ++++---- > > arch/x86/kernel/alternative.c | 8 +++++--- > > 3 files changed, 14 insertions(+), 12 deletions(-) > > > >diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h > >index 2851bc2339d5..e56065ea73f2 100644 > >--- a/arch/x86/include/asm/paravirt.h > >+++ b/arch/x86/include/asm/paravirt.h > >@@ -735,16 +735,16 @@ extern void default_banner(void); > > > > #else /* __ASSEMBLY__ */ > > > >-#define _PVSITE(ptype, ops, word, algn) \ > >+#define _PVSITE(ptype, ops) \ > > 771:; \ > > ops; \ > > 772:; \ > > .pushsection .parainstructions,"a"; \ > >- .align algn; \ > >- word 771b; \ > >+ .align 4; \ > >+ .long 771b-.; \ > > .byte ptype; \ > > .byte 772b-771b; \ > >- _ASM_ALIGN; \ > >+ .align 4; \ > > .popsection > > > > > >@@ -752,7 +752,7 @@ extern void default_banner(void); > > #ifdef CONFIG_PARAVIRT_XXL > > > > #define PARA_PATCH(off) ((off) / 8) > >-#define PARA_SITE(ptype, ops) _PVSITE(ptype, ops, .quad, 8) > >+#define PARA_SITE(ptype, ops) _PVSITE(ptype, ops) > > #define PARA_INDIRECT(addr) *addr(%rip) > > > > #ifdef CONFIG_DEBUG_ENTRY > >diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h > >index 8c1da419260f..68952ae07a3f 100644 > >--- a/arch/x86/include/asm/paravirt_types.h > >+++ b/arch/x86/include/asm/paravirt_types.h > >@@ -5,7 +5,7 @@ > > #ifndef __ASSEMBLY__ > > /* These all sit in the .parainstructions section to tell us what to patch. */ > > struct paravirt_patch_site { > >- u8 *instr; /* original instructions */ > >+ s32 instr_offset; /* original instructions */ > > u8 type; /* type of this instruction */ > > u8 len; /* length of original instruction */ > > }; > >@@ -273,11 +273,11 @@ extern struct paravirt_patch_template pv_ops; > > #define _paravirt_alt(insn_string, type) \ > > "771:\n\t" insn_string "\n" "772:\n" \ > > ".pushsection .parainstructions,\"a\"\n" \ > >- _ASM_ALIGN "\n" \ > >- _ASM_PTR " 771b\n" \ > >+ " .align 4\n" \ > >+ " .long 771b-.\n" \ > > " .byte " type "\n" \ > > " .byte 772b-771b\n" \ > >- _ASM_ALIGN "\n" \ > >+ " .align 4\n" \ > > ".popsection\n" > > > > /* Generate patchable code, with the default asm parameters. */ > >diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > >index 111b809f0ac2..6eea563a098d 100644 > >--- a/arch/x86/kernel/alternative.c > >+++ b/arch/x86/kernel/alternative.c > >@@ -1232,20 +1232,22 @@ void __init_or_module apply_paravirt(struct paravirt_patch_site *start, > > { > > struct paravirt_patch_site *p; > > char insn_buff[MAX_PATCH_LEN]; > >+ u8 *instr; > > > > for (p = start; p < end; p++) { > > unsigned int used; > > > >+ instr = (u8 *)&p->instr_offset + p->instr_offset; > > BUG_ON(p->len > MAX_PATCH_LEN); > > /* prep the buffer with the original instructions */ > >- memcpy(insn_buff, p->instr, p->len); > >- used = paravirt_patch(p->type, insn_buff, (unsigned long)p->instr, p->len); > >+ memcpy(insn_buff, instr, p->len); > >+ used = paravirt_patch(p->type, insn_buff, (unsigned long)instr, p->len); > > > > BUG_ON(used > p->len); > > > > /* Pad the rest with nops */ > > add_nops(insn_buff + used, p->len - used); > >- text_poke_early(p->instr, insn_buff, p->len); > >+ text_poke_early(instr, insn_buff, p->len); > > } > > } > > extern struct paravirt_patch_site __start_parainstructions[], > > Any reason that you couldn't use the same patching code?
Sorry, what do you mean using the same patching code? Do you mean that share some code between apply_alternatives() and apply_paravirt()?
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