From: Borislav Petkov <bp@alien8.de>
To: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Babu Moger <babu.moger@amd.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <seanjc@google.com>,
David.Kaplan@amd.com, Andrew Cooper <andrew.cooper3@citrix.com>,
Nikolay Borisov <nik.borisov@suse.com>,
gregkh@linuxfoundation.org, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 12/22] x86/srso: Remove redundant X86_FEATURE_ENTRY_IBPB check
Date: Fri, 25 Aug 2023 09:09:36 +0200 [thread overview]
Message-ID: <20230825070936.GEZOhTsPiTLhY1i9xH@fat_crate.local> (raw)
In-Reply-To: <bb018289827a8709d11b22f28345690753597fa5.1692580085.git.jpoimboe@kernel.org>
On Sun, Aug 20, 2023 at 06:19:09PM -0700, Josh Poimboeuf wrote:
> The X86_FEATURE_ENTRY_IBPB check is redundant here due to the above
> RETBLEED_MITIGATION_IBPB check. RETBLEED_MITIGATION_IBPB already
> implies X86_FEATURE_ENTRY_IBPB. So if we got here and 'has_microcode'
> is true, it means X86_FEATURE_ENTRY_IBPB is not set.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.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 b27aeb86ed7a..aeddd5ce9f34 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -2475,7 +2475,7 @@ static void __init srso_select_mitigation(void)
>
> case SRSO_CMD_IBPB_ON_VMEXIT:
> if (IS_ENABLED(CONFIG_CPU_SRSO)) {
> - if (!boot_cpu_has(X86_FEATURE_ENTRY_IBPB) && has_microcode) {
> + if (has_microcode) {
> setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
> srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT;
> }
Well, frankly, I'd prefer to keep this check explicit as it is also
documenting the situation. And it is also protecting against future,
potential mistakes done while refactoring. And it is not such a complex
condition so that it stands in the way and makes the code too
unreadable, while removing it makes it a bit too subtle considering the
amazing maze we're in.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2023-08-25 7:10 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-21 1:18 [PATCH 00/22] SRSO fixes/cleanups Josh Poimboeuf
2023-08-21 1:18 ` [PATCH 01/22] x86/srso: Fix srso_show_state() side effect Josh Poimboeuf
2023-08-21 5:42 ` Nikolay Borisov
2023-08-21 6:04 ` Borislav Petkov
2023-08-21 16:17 ` Josh Poimboeuf
2023-08-22 5:23 ` Borislav Petkov
2023-08-21 1:18 ` [PATCH 02/22] x86/srso: Set CPUID feature bits independently of bug or mitigation status Josh Poimboeuf
2023-08-21 5:42 ` Nikolay Borisov
2023-08-21 9:27 ` Andrew Cooper
2023-08-21 14:06 ` Borislav Petkov
2023-08-23 5:20 ` Borislav Petkov
2023-08-23 12:22 ` Andrew Cooper
2023-08-24 4:24 ` Borislav Petkov
2023-08-24 22:04 ` Josh Poimboeuf
2023-08-25 6:42 ` Borislav Petkov
2023-08-21 13:59 ` Borislav Petkov
2023-08-21 1:19 ` [PATCH 03/22] KVM: x86: Support IBPB_BRTYPE and SBPB Josh Poimboeuf
2023-08-21 9:34 ` Andrew Cooper
2023-08-21 16:23 ` Josh Poimboeuf
2023-08-21 16:35 ` Sean Christopherson
2023-08-21 16:46 ` Nikolay Borisov
2023-08-21 16:50 ` Sean Christopherson
2023-08-21 17:05 ` Josh Poimboeuf
2023-08-24 16:39 ` Sean Christopherson
2023-08-24 17:07 ` Josh Poimboeuf
2023-08-21 16:49 ` Sean Christopherson
2023-08-21 1:19 ` [PATCH 04/22] x86/srso: Fix SBPB enablement for spec_rstack_overflow=off Josh Poimboeuf
2023-08-21 14:16 ` Borislav Petkov
2023-08-21 16:36 ` Josh Poimboeuf
2023-08-22 5:54 ` Borislav Petkov
2023-08-22 6:07 ` Borislav Petkov
2023-08-22 21:59 ` Josh Poimboeuf
2023-08-23 1:27 ` Borislav Petkov
2023-08-21 1:19 ` [PATCH 05/22] x86/srso: Fix SBPB enablement for mitigations=off Josh Poimboeuf
2023-08-23 5:57 ` Borislav Petkov
2023-08-23 20:55 ` Josh Poimboeuf
2023-08-23 23:02 ` Josh Poimboeuf
2023-08-21 1:19 ` [PATCH 06/22] x86/srso: Print actual mitigation if requested mitigation isn't possible Josh Poimboeuf
2023-08-23 6:06 ` Borislav Petkov
2023-08-21 1:19 ` [PATCH 07/22] x86/srso: Remove default case in srso_select_mitigation() Josh Poimboeuf
2023-08-23 6:18 ` Borislav Petkov
2023-08-21 1:19 ` [PATCH 08/22] x86/srso: Downgrade retbleed IBPB warning to informational message Josh Poimboeuf
2023-08-24 4:43 ` Borislav Petkov
2023-08-21 1:19 ` [PATCH 09/22] x86/srso: Simplify exit paths Josh Poimboeuf
2023-08-21 1:19 ` [PATCH 10/22] x86/srso: Print mitigation for retbleed IBPB case Josh Poimboeuf
2023-08-24 4:48 ` Borislav Petkov
2023-08-24 21:40 ` Josh Poimboeuf
2023-08-21 1:19 ` [PATCH 11/22] x86/srso: Slight simplification Josh Poimboeuf
2023-08-24 4:55 ` Borislav Petkov
2023-08-21 1:19 ` [PATCH 12/22] x86/srso: Remove redundant X86_FEATURE_ENTRY_IBPB check Josh Poimboeuf
2023-08-25 7:09 ` Borislav Petkov [this message]
2023-08-21 1:19 ` [PATCH 13/22] x86/srso: Fix vulnerability reporting for missing microcode Josh Poimboeuf
2023-08-25 7:25 ` Borislav Petkov
2023-08-21 1:19 ` [PATCH 14/22] x86/srso: Fix unret validation dependencies Josh Poimboeuf
2023-08-21 1:19 ` [PATCH 15/22] x86/alternatives: Remove faulty optimization Josh Poimboeuf
2023-08-21 1:19 ` [PATCH 16/22] x86/srso: Unexport untraining functions Josh Poimboeuf
2023-08-21 5:50 ` Nikolay Borisov
2023-08-21 1:19 ` [PATCH 17/22] x86/srso: Disentangle rethunk-dependent options Josh Poimboeuf
2023-08-21 1:19 ` [PATCH 18/22] x86/rethunk: Use SYM_CODE_START[_LOCAL]_NOALIGN macros Josh Poimboeuf
2023-08-21 1:19 ` [PATCH 19/22] x86/srso: Improve i-cache locality for alias mitigation Josh Poimboeuf
2023-08-21 1:19 ` [PATCH 20/22] x86/retpoline: Remove .text..__x86.return_thunk section Josh Poimboeuf
2023-08-21 1:19 ` [PATCH 21/22] x86/nospec: Refactor UNTRAIN_RET[_*] Josh Poimboeuf
2023-08-21 1:19 ` [PATCH 22/22] x86/calldepth: Rename __x86_return_skl() to call_depth_return_thunk() Josh Poimboeuf
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