From: Borislav Petkov <bp@alien8.de>
To: Juergen Gross <jgross@suse.com>
Cc: xen-devel@lists.xenproject.org, x86@kernel.org,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v3 07/15] x86/alternative: support "not feature" and ALTERNATIVE_TERNARY
Date: Thu, 7 Jan 2021 20:08:19 +0100 [thread overview]
Message-ID: <20210107190819.GI14697@zn.tnic> (raw)
In-Reply-To: <20201217093133.1507-8-jgross@suse.com>
On Thu, Dec 17, 2020 at 10:31:25AM +0100, Juergen Gross wrote:
> Instead of only supporting to modify instructions when a specific
> feature is set, support doing so for the case a feature is not set.
>
> As today a feature is specified using a 16 bit quantity and the highest
> feature number in use is around 600, using a negated feature number for
> specifying the inverted case seems to be appropriate.
>
> ALTERNATIVE "default_instr", "patched_instr", ~FEATURE_NR
>
> will start with "default_instr" and patch that with "patched_instr" in
> case FEATURE_NR is not set.
>
> Using that add ALTERNATIVE_TERNARY:
>
> ALTERNATIVE_TERNARY "default_instr", FEATURE_NR,
> "feature_on_instr", "feature_off_instr"
>
> which will start with "default_instr" and at patch time will, depending
> on FEATURE_NR being set or not, patch that with either
> "feature_on_instr" or "feature_off_instr".
How about an even simpler one (only build-tested):
---
diff --git a/arch/x86/include/asm/alternative-asm.h b/arch/x86/include/asm/alternative-asm.h
index 464034db299f..d52b423d3cab 100644
--- a/arch/x86/include/asm/alternative-asm.h
+++ b/arch/x86/include/asm/alternative-asm.h
@@ -109,6 +109,9 @@
.popsection
.endm
+#define ALTERNATIVE_TERNARY(oldinstr, feature, newinstr1, newinstr2) \
+ ALTERNATIVE_2 oldinstr, newinstr1, feature, newinstr2, X86_FEATURE_TERNARY
+
#endif /* __ASSEMBLY__ */
#endif /* _ASM_X86_ALTERNATIVE_ASM_H */
diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 13adca37c99a..f170cbe89539 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -175,6 +175,9 @@ static inline int alternatives_text_reserved(void *start, void *end)
ALTINSTR_REPLACEMENT(newinstr2, feature2, 2) \
".popsection\n"
+#define ALTERNATIVE_TERNARY(oldinstr, feature, newinstr1, newinstr2) \
+ ALTERNATIVE_2(oldinstr, newinstr1, feature, newinstr2, X86_FEATURE_TERNARY)
+
#define ALTERNATIVE_3(oldinsn, newinsn1, feat1, newinsn2, feat2, newinsn3, feat3) \
OLDINSTR_3(oldinsn, 1, 2, 3) \
".pushsection .altinstructions,\"a\"\n" \
@@ -206,6 +209,9 @@ static inline int alternatives_text_reserved(void *start, void *end)
#define alternative_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
asm_inline volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) ::: "memory")
+#define alternative_ternary(oldinstr, feature, newinstr1, newinstr2) \
+ asm_inline volatile(ALTERNATIVE_TERNARY(oldinstr, feature, newinstr1, newinstr2) ::: "memory")
+
/*
* Alternative inline assembly with input.
*
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 84b887825f12..cc634db0b91f 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -108,7 +108,7 @@
#define X86_FEATURE_EXTD_APICID ( 3*32+26) /* Extended APICID (8 bits) */
#define X86_FEATURE_AMD_DCM ( 3*32+27) /* AMD multi-node processor */
#define X86_FEATURE_APERFMPERF ( 3*32+28) /* P-State hardware coordination feedback capability (APERF/MPERF MSRs) */
-/* free ( 3*32+29) */
+#define X86_FEATURE_TERNARY ( 3*32+29) /* "" Synthetic bit for ALTERNATIVE_TERNARY() */
#define X86_FEATURE_NONSTOP_TSC_S3 ( 3*32+30) /* TSC doesn't stop in S3 state */
#define X86_FEATURE_TSC_KNOWN_FREQ ( 3*32+31) /* TSC has known frequency */
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 8d778e46725d..2cb29d4d8dd9 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -393,7 +393,7 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
replacement = (u8 *)&a->repl_offset + a->repl_offset;
BUG_ON(a->instrlen > sizeof(insn_buff));
BUG_ON(a->cpuid >= (NCAPINTS + NBUGINTS) * 32);
- if (!boot_cpu_has(a->cpuid)) {
+ if (!boot_cpu_has(a->cpuid) && (a->cpuid != X86_FEATURE_TERNARY)) {
if (a->padlen > 1)
optimize_nops(a, instr);
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2021-01-07 19:09 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-17 9:31 [PATCH v3 00/15] x86: major paravirt cleanup Juergen Gross
2020-12-17 9:31 ` [PATCH v3 01/15] x86/xen: use specific Xen pv interrupt entry for MCE Juergen Gross
2020-12-17 9:31 ` [PATCH v3 02/15] x86/xen: use specific Xen pv interrupt entry for DF Juergen Gross
2020-12-17 9:31 ` [PATCH v3 03/15] x86/pv: switch SWAPGS to ALTERNATIVE Juergen Gross
2020-12-17 9:31 ` [PATCH v3 04/15] x86/xen: drop USERGS_SYSRET64 paravirt call Juergen Gross
2020-12-17 9:31 ` [PATCH v3 05/15] x86: rework arch_local_irq_restore() to not use popf Juergen Gross
2020-12-17 9:31 ` [PATCH v3 06/15] x86/paravirt: switch time pvops functions to use static_call() Juergen Gross
2020-12-17 17:31 ` Michael Kelley
2021-01-06 10:41 ` Borislav Petkov
2021-01-19 11:36 ` Jürgen Groß
2021-01-06 10:03 ` Borislav Petkov
2021-01-19 11:33 ` Jürgen Groß
2020-12-17 9:31 ` [PATCH v3 07/15] x86/alternative: support "not feature" and ALTERNATIVE_TERNARY Juergen Gross
2021-01-07 19:08 ` Borislav Petkov [this message]
2021-01-19 11:35 ` Jürgen Groß
2021-01-19 12:06 ` Borislav Petkov
2021-01-19 12:12 ` Jürgen Groß
2020-12-17 9:31 ` [PATCH v3 08/15] x86: add new features for paravirt patching Juergen Gross
2020-12-17 13:12 ` kernel test robot
2021-01-14 18:30 ` Borislav Petkov
2021-01-14 18:40 ` Borislav Petkov
2020-12-17 9:31 ` [PATCH v3 09/15] x86/paravirt: remove no longer needed 32-bit pvops cruft Juergen Gross
2020-12-17 9:31 ` [PATCH v3 10/15] x86/paravirt: simplify paravirt macros Juergen Gross
2020-12-17 16:46 ` kernel test robot
2020-12-17 9:31 ` [PATCH v3 11/15] x86/paravirt: switch iret pvops to ALTERNATIVE Juergen Gross
2020-12-17 9:31 ` [PATCH v3 12/15] objtool: Alternatives vs ORC, the hard way Juergen Gross
2020-12-17 9:31 ` [PATCH v3 13/15] x86/paravirt: add new macros PVOP_ALT* supporting pvops in ALTERNATIVEs Juergen Gross
2020-12-17 9:31 ` [PATCH v3 14/15] x86/paravirt: switch functions with custom code to ALTERNATIVE Juergen Gross
2020-12-17 16:42 ` kernel test robot
2020-12-17 9:31 ` [PATCH v3 15/15] x86/paravirt: have only one paravirt patch function Juergen Gross
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