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Message-ID: <20230814202545.GKZNqNybUnKv+xyrtP@fat_crate.local>
Date: Mon, 14 Aug 2023 22:25:45 +0200
From: Borislav Petkov <bp@...en8.de>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Nikolay Borisov <nik.borisov@...e.com>, X86 ML <x86@...nel.org>,
Josh Poimboeuf <jpoimboe@...hat.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/srso: Disable the mitigation on unaffected
configurations
On Mon, Aug 14, 2023 at 01:08:13PM -0700, Josh Poimboeuf wrote:
> Tangentially, the 'cpu_smt_control == CPU_SMT_DISABLED' check is wrong,
> as SMT could still get enabled at runtime and SRSO would be exposed.
Well, even if it gets exposed, I don't think we can safely enable the
mitigation at runtime as alternatives have run already.
I guess I could use CPU_SMT_FORCE_DISABLED here.
> Also is there a reason to re-use the hardware SRSO_NO bit
Not a hardware bit - this is set by software - it is only allocated in
the CPUID leaf for easier interaction with guests.
> rather than clear the bug bit?
We don't clear the X86_BUGs. Ever. The logic is that if the CPU matches
an affected CPU, that flag remains to show that it is potentially
affected.
/sys/devices/system/cpu/vulnerabilities/ tells you what the actual state
is.
> That seems cleaner, then you wouldn't need this hack:
Not a hack. This is just like the other "not affected" feature flags.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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