From: Borislav Petkov <bp@alien8.de>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>,
linux-kernel@vger.kernel.org, x86@kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Asish Kalra <ashish.kalra@amd.com>,
Michael Roth <michael.roth@amd.com>,
Joerg Roedel <jroedel@suse.de>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
stable@vger.kernel.org, Sean Christopherson <seanjc@google.com>
Subject: Re: [PATCH] x86/sev: Don't use cc_platform_has() for early SEV-SNP calls
Date: Wed, 24 Aug 2022 20:48:44 +0200 [thread overview]
Message-ID: <YwZyjE6BmnvxHXcR@zn.tnic> (raw)
In-Reply-To: <10bc452f-3564-e41b-836d-e135a8f4260d@intel.com>
On Wed, Aug 24, 2022 at 11:43:10AM -0700, Dave Hansen wrote:
> So, we don't have *ANY* control over where the compiler uses jump
> tables. The kernel just happened to add some code that uses them, fell
> over, and this adds a hack to get booting again.
>
> Isn't this a bigger problem?
I had the same question already. Was thinking of maybe disabling
the compiler from producing jump tables in the ident-mapped code.
Tom's argument is that that might prevent the compiler from doing
optimizations but I haven't talked to compiler folks whether those
optimizations are even worth the effort.
Regardless, the potential problem is limited:
"# (jump-tables are implicitly disabled by RETPOLINE)"
i.e., only RETPOLINE=n builds for now which should be a minority?
I guess when this explodes somewhere else again, we will have to
generalize a fix.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2022-08-24 18:48 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-23 21:55 Tom Lendacky
2022-08-24 18:43 ` Dave Hansen
2022-08-24 18:48 ` Borislav Petkov [this message]
2022-08-24 18:53 ` Dave Hansen
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