From: "Jürgen Groß" <jgross@suse.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
llvm@lists.linux.dev, xin@zytor.com,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <nick.desaulniers+lkml@gmail.com>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>
Subject: Re: [PATCH v2 09/12] x86/msr: Use the alternatives mechanism for WRMSR
Date: Tue, 30 Sep 2025 17:42:13 +0200 [thread overview]
Message-ID: <2ad137cb-ed38-42f6-ac0a-a81569051779@suse.com> (raw)
In-Reply-To: <20250930125156.GK1386988@noisy.programming.kicks-ass.net>
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On 30.09.25 14:51, Peter Zijlstra wrote:
> On Tue, Sep 30, 2025 at 10:50:44AM +0200, Peter Zijlstra wrote:
>> On Tue, Sep 30, 2025 at 10:46:23AM +0200, Jürgen Groß wrote:
>
>>>> asm_inline volatile goto(
>>>> "1:\n"
>>>> ALTERNATIVE(PREPARE_RCX_RDX_FOR_WRMSR
>>>> "2:\n"
>>>> ALTERNATIVE("ds wrmsr",
>>>> ASM_WRMSRNS, X86_FEATURE_WRMSRNS),
>>>> ASM_WRMSRNS_IMM, X86_FEATURE_MSR_IMM);
>>>> _ASM_EXTABLE_TYPE(1b, %l[badmsr], %c[type]) /* For WRMSRNS immediate */
>>>> _ASM_EXTABLE_TYPE(2b, %l[badmsr], %c[type]) /* For WRMSR(NS) */
>>>>
>>>> :
>>>> : [val] "a" (val), [msr] "i" (msr), [type] "i" (type)
>>>> : "memory", "ecx", "rdx"
>>>> : badmsr);
>>>>
>
>> Oh well, lets forget about this :-)
>
> So I couldn't. I tried the below, which when building a .i generates the
> following:
>
>
> static inline __attribute__((__gnu_inline__)) __attribute__((__unused__)) __attribute__((no_instrument_function)) void clear_page(void *page)
> {
>
> kmsan_unpoison_memory(page, ((1UL) << 12));
> asm __inline volatile(
> "# ALT: oldinstr\n"
> "__UNIQUE_ID_altinstr_9" "_begin:\n\t"
>
> "# ALT: oldinstr\n"
> "__UNIQUE_ID_altinstr_8" "_begin:\n\t"
> "call %c[old]" "\n"
> "__UNIQUE_ID_altinstr_8" "_pad:\n"
> "# ALT: padding\n"
> ".skip -(((" "__UNIQUE_ID_altinstr_8" "_alt_end - " "__UNIQUE_ID_altinstr_8" "_alt_begin" ")-(" "__UNIQUE_ID_altinstr_8" "_pad - " "__UNIQUE_ID_altinstr_8" "_begin" ")) > 0) * "
> "((" "__UNIQUE_ID_altinstr_8" "_alt_end - " "__UNIQUE_ID_altinstr_8" "_alt_begin" ")-(" "__UNIQUE_ID_altinstr_8" "_pad - " "__UNIQUE_ID_altinstr_8" "_begin" ")),0x90\n"
> "__UNIQUE_ID_altinstr_8" "_end:\n"
> ".pushsection .altinstructions,\"a\"\n"
> " .long " "__UNIQUE_ID_altinstr_8" "_begin - .\n"
> " .long " "__UNIQUE_ID_altinstr_8" "_alt_begin - .\n"
> " .4byte " "( 3*32+16)" "\n"
> " .byte " "__UNIQUE_ID_altinstr_8" "_end - " "__UNIQUE_ID_altinstr_8" "_begin" "\n"
> " .byte " "__UNIQUE_ID_altinstr_8" "_alt_end - " "__UNIQUE_ID_altinstr_8" "_alt_begin" "\n"
> ".popsection\n"
> ".pushsection .altinstr_replacement, \"ax\"\n"
> "# ALT: replacement\n"
> "__UNIQUE_ID_altinstr_8" "_alt_begin:\n\t"
> "call %c[new1]" "\n"
> "__UNIQUE_ID_altinstr_8" "_alt_end:\n"
> ".popsection\n"
> "\n"
>
> "__UNIQUE_ID_altinstr_9" "_pad:\n"
> "# ALT: padding\n"
> ".skip -(((" "__UNIQUE_ID_altinstr_9" "_alt_end - " "__UNIQUE_ID_altinstr_9" "_alt_begin" ")-(" "__UNIQUE_ID_altinstr_9" "_pad - " "__UNIQUE_ID_altinstr_9" "_begin" ")) > 0) * "
> "((" "__UNIQUE_ID_altinstr_9" "_alt_end - " "__UNIQUE_ID_altinstr_9" "_alt_begin" ")-(" "__UNIQUE_ID_altinstr_9" "_pad - " "__UNIQUE_ID_altinstr_9" "_begin" ")),0x90\n"
> "__UNIQUE_ID_altinstr_9" "_end:\n"
> ".pushsection .altinstructions,\"a\"\n"
> " .long " "__UNIQUE_ID_altinstr_9" "_begin - .\n"
> " .long " "__UNIQUE_ID_altinstr_9" "_alt_begin - .\n"
> " .4byte " "( 9*32+ 9)" "\n"
> " .byte " "__UNIQUE_ID_altinstr_9" "_end - " "__UNIQUE_ID_altinstr_9" "_begin" "\n"
> " .byte " "__UNIQUE_ID_altinstr_9" "_alt_end - " "__UNIQUE_ID_altinstr_9" "_alt_begin" "\n"
> ".popsection\n"
> ".pushsection .altinstr_replacement, \"ax\"\n"
> "# ALT: replacement\n"
> "__UNIQUE_ID_altinstr_9" "_alt_begin:\n\t"
> "call %c[new2]" "\n"
> "__UNIQUE_ID_altinstr_9" "_alt_end:\n"
> ".popsection\n"
> : "+r" (current_stack_pointer), "=D" (page)
> : [old] "i" (clear_page_orig), [new1] "i" (clear_page_rep), [new2] "i" (clear_page_erms) , "D" (page)
> : "cc", "memory", "rax", "rcx")
>
> ;
> }
>
> Which looks right, but utterly fails to build :(
What does the failure look like?
Could it be that the labels should be local ones?
Juergen
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next prev parent reply other threads:[~2025-09-30 15:42 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-30 7:03 [PATCH v2 00/12] x86/msr: Inline rdmsr/wrmsr instructions Juergen Gross
2025-09-30 7:03 ` [PATCH v2 09/12] x86/msr: Use the alternatives mechanism for WRMSR Juergen Gross
2025-09-30 8:31 ` Peter Zijlstra
2025-09-30 8:46 ` Jürgen Groß
2025-09-30 8:50 ` Peter Zijlstra
2025-09-30 12:51 ` Peter Zijlstra
2025-09-30 15:42 ` Jürgen Groß [this message]
2025-10-01 6:43 ` Peter Zijlstra
2025-10-01 7:23 ` Peter Zijlstra
2025-10-03 14:23 ` Dave Hansen
2025-10-03 16:53 ` H. Peter Anvin
2025-10-01 8:49 ` Juergen Gross
2025-10-01 10:50 ` Peter Zijlstra
2025-10-01 11:16 ` Jürgen Groß
2025-09-30 16:00 ` Sean Christopherson
2025-10-01 9:13 ` Jürgen Groß
2025-09-30 19:19 ` [PATCH v2 00/12] x86/msr: Inline rdmsr/wrmsr instructions H. Peter Anvin
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