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 [PATCH] x86/sev: Don't use cc_platform_has() for early SEV-SNP calls 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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YwZyjE6BmnvxHXcR@zn.tnic \
--to=bp@alien8.de \
--cc=ashish.kalra@amd.com \
--cc=dave.hansen@intel.com \
--cc=dave.hansen@linux.intel.com \
--cc=hpa@zytor.com \
--cc=jroedel@suse.de \
--cc=kirill@shutemov.name \
--cc=linux-kernel@vger.kernel.org \
--cc=michael.roth@amd.com \
--cc=mingo@redhat.com \
--cc=seanjc@google.com \
--cc=stable@vger.kernel.org \
--cc=tglx@linutronix.de \
--cc=thomas.lendacky@amd.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.