From: David Woodhouse <dwmw2@infradead.org>
To: Andi Kleen <ak@linux.intel.com>
Cc: Paul Turner <pjt@google.com>, LKML <linux-kernel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linux-foundation.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
Dave Hansen <dave.hansen@intel.com>,
tglx@linutronix.de, Kees Cook <keescook@google.com>,
Rik van Riel <riel@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@amacapital.net>,
Jiri Kosina <jikos@kernel.org>,
gnomes@lxorguk.ukuu.org.uk, x86@kernel.org,
thomas.lendacky@amd.com, Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH] x86/retpoline: Fill RSB on context switch for affected CPUs
Date: Fri, 12 Jan 2018 18:23:07 +0000 [thread overview]
Message-ID: <1515781387.22302.472.camel@infradead.org> (raw)
In-Reply-To: <20180112180224.GP6718@tassilo.jf.intel.com>
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On Fri, 2018-01-12 at 10:02 -0800, Andi Kleen wrote:
> > + if ((!boot_cpu_has(X86_FEATURE_PTI) &&
> > + !boot_cpu_has(X86_FEATURE_SMEP)) || is_skylake_era()) {
> > + setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW);
> > + pr_info("Filling RSB on context switch\n");
>
> We need to do more things for Skylake (like idle and interrupt fill
> and possibly deep call cahin), so I don't think it makes sense to
>
> - have an individual flag for each of these. It can be just a single
> flag that enables all of this for Skylake
>
> - print something for each of them. that will just be very noisy
> without any useful benefit to the user.
I still think we are better off using IBRS by default on Skylake.
This patch wasn't really for Skylake; the real use case was for AMD
CPUs (!PTI) without SMEP. Since it happens to needed on Skylake too we
might as well enable it there... but that doesn't mean I was planning
to do all the other horrible crap we need for Skylake.
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next prev parent reply other threads:[~2018-01-12 18:23 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-12 17:49 [PATCH] x86/retpoline: Fill RSB on context switch for affected CPUs David Woodhouse
2018-01-12 18:02 ` Andi Kleen
2018-01-12 18:23 ` David Woodhouse [this message]
2018-01-12 18:05 ` Andrew Cooper
2018-01-12 18:56 ` David Woodhouse
2018-01-12 23:41 ` Josh Poimboeuf
2018-01-14 11:39 ` Thomas Gleixner
2018-01-14 17:04 ` [tip:x86/pti] " tip-bot for David Woodhouse
2018-01-15 14:35 ` David Laight
2018-01-15 14:39 ` David Woodhouse
2018-01-15 14:42 ` Arjan van de Ven
2018-01-15 20:03 ` Kees Cook
2018-01-14 23:37 ` tip-bot for David Woodhouse
2018-01-15 0:05 ` Andi Kleen
2018-01-15 0:09 ` Andi Kleen
2018-01-15 10:13 ` David Woodhouse
2018-03-09 13:12 ` Maciej S. Szmigiero
2018-03-09 15:14 ` Andi Kleen
2018-03-09 15:33 ` Maciej S. Szmigiero
2018-03-09 15:38 ` Woodhouse, David
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