linux-kernel - Re: [PATCH 01/22] x86/srso: Fix srso_show

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Message-ID: <d0cee6c4-5598-3b69-d99b-6020fdd67f51@suse.com>
Date:   Mon, 21 Aug 2023 08:42:38 +0300
From:   Nikolay Borisov <nik.borisov@...e.com>
To:     Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Babu Moger <babu.moger@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>, David.Kaplan@....com,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        gregkh@...uxfoundation.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 01/22] x86/srso: Fix srso_show_state() side effect



On 21.08.23 г. 4:18 ч., Josh Poimboeuf wrote:
> Reading the 'spec_rstack_overflow' sysfs file can trigger an unnecessary
> MSR write, and possibly even a (handled) exception if the microcode
> hasn't been updated.
> 
> Avoid all that by just checking X86_FEATURE_IBPB_BRTYPE instead, which
> gets set by srso_select_mitigation() if the updated microcode exists.
> 
> Fixes: fb3bd914b3ec ("x86/srso: Add a Speculative RAS Overflow mitigation")
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> ---
>   arch/x86/kernel/cpu/bugs.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index f081d26616ac..bdd3e296f72b 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -2717,7 +2717,7 @@ static ssize_t srso_show_state(char *buf)
>   
>   	return sysfs_emit(buf, "%s%s\n",
>   			  srso_strings[srso_mitigation],
> -			  (cpu_has_ibpb_brtype_microcode() ? "" : ", no microcode"));
> +			  boot_cpu_has(X86_FEATURE_IBPB_BRTYPE) ? "" : ", no microcode");
>   }
>   
>   static ssize_t gds_show_state(char *buf)


Reviewed-by: Nikolay Borisov <nik.borisov@...e.com>