Messages in this thread | | | Date | Thu, 24 Nov 2022 19:06:53 +0800 | From | "Hou Wenlong" <> | Subject | Re: [PATCH] x86/paravirt: Use relative reference for original instruction |
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On Thu, Nov 24, 2022 at 11:18:52AM +0100, Juergen Gross wrote: > On 24.11.22 09:51, Hou Wenlong 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 > > 8 bytes saved? I think those are 4 bytes only. > The corresponding C structure paravirt_patch_site is not packed, Before this, its size is 16 bytes in x86_64,due to the alignment of 8 bytes. Now the alignment is 4 bytes, so the size is 8 bytes.
> >R_X86_64_64 relocation, which also reduces relocation metadata on > >relocatable builds. > > > >Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com> > >--- > > arch/x86/include/asm/paravirt.h | 6 +++--- > > arch/x86/include/asm/paravirt_types.h | 4 ++-- > > arch/x86/kernel/alternative.c | 8 +++++--- > > 3 files changed, 10 insertions(+), 8 deletions(-) > > > >diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h > >index 2851bc2339d5..2cbe9b64e103 100644 > >--- a/arch/x86/include/asm/paravirt.h > >+++ b/arch/x86/include/asm/paravirt.h > >@@ -735,13 +735,13 @@ extern void default_banner(void); > > #else /* __ASSEMBLY__ */ > >-#define _PVSITE(ptype, ops, word, algn) \ > >+#define _PVSITE(ptype, ops, algn) \ > > Would you please drop the algn parameter, too? It isn't needed anymore > as the alignment can be hard coded to be 4 now. This would need to be > adjusted in the _paravirt_alt() macro, too. > OK, since the aligment is 4 bytes now, it seems that _ASM_ALIGN could be dropped too?
> > 771:; \ > > ops; \ > > 772:; \ > > .pushsection .parainstructions,"a"; \ > > .align algn; \ > >- word 771b; \ > >+ .long 771b-.; \ > > .byte ptype; \ > > .byte 772b-771b; \ > > _ASM_ALIGN; \ > >@@ -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, 8) > > #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..19f709cf7df9 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 */ > > }; > >@@ -274,7 +274,7 @@ extern struct paravirt_patch_template pv_ops; > > "771:\n\t" insn_string "\n" "772:\n" \ > > ".pushsection .parainstructions,\"a\"\n" \ > > _ASM_ALIGN "\n" \ > >- _ASM_PTR " 771b\n" \ > >+ " .long 771b-.\n" \ > > " .byte " type "\n" \ > > " .byte 772b-771b\n" \ > > _ASM_ALIGN "\n" \ > >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[], > > > Juergen
> pub 2048R/28BF132F 2014-06-02 Juergen Gross <jg@pfupf.net> > uid Juergen Gross <jgross@suse.com> > uid Juergen Gross <jgross@novell.com> > uid Juergen Gross <jgross@suse.de> > sub 2048R/16375B53 2014-06-02
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