From: "Woodhouse, David" <dwmw@amazon.co.uk>
To: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
"tim.c.chen@linux.intel.com" <tim.c.chen@linux.intel.com>
Cc: "mingo@kernel.org" <mingo@kernel.org>,
"peterz@infradead.org" <peterz@infradead.org>,
"arjan@linux.intel.com" <arjan@linux.intel.com>,
"Raslan, KarimAllah" <karahmed@amazon.de>,
"torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"nadav.amit@gmail.com" <nadav.amit@gmail.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"stable@vger.kernel.org" <stable@vger.kernel.org>,
"ak@linux.intel.com" <ak@linux.intel.com>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"riel@redhat.com" <riel@redhat.com>,
"luto@kernel.org" <luto@kernel.org>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"bp@alien8.de" <bp@alien8.de>,
"dave.hansen@intel.com" <dave.hansen@intel.com>,
"mgorman@suse.de" <mgorman@suse.de>
Subject: Re: [PATCH 0/2] Backport IBPB on context switch to non-dumpable process
Date: Sat, 3 Mar 2018 11:37:56 +0000 [thread overview]
Message-ID: <1520077075.7929.4.camel@amazon.co.uk> (raw)
In-Reply-To: <20180303085454.GA23988@kroah.com>
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On Sat, 2018-03-03 at 09:54 +0100, Greg Kroah-Hartman wrote:
> On Fri, Mar 02, 2018 at 01:32:08PM -0800, Tim Chen wrote:
> >
> > Greg,
> >
> > I will like to propose backporting "x86/speculation: Use Indirect Branch
> > Prediction Barrier on context switch" from commit 18bf3c3e in upstream
> > to 4.9 and 4.4 stable. The patch has already been ported to 4.14 and
> > 4.15 stable. The patch needs mm context id that Andy added in commit
> > f39681ed. I have lifted the mm context id change from Andy's upstream
> > patch and included it here.
>
> What does this patch "fix" in those older kernels? Is this a
> performance improvement or something else?
It's part of the Spectre variant 2 mitigation — a full flush of the
branch prediction on context switch to a sensitive¹ process. It was the
one I called out as "needs more attention" when I did the rest of the
retpoline etc backportingk, and Tim has now fixed it up. (Thanks).
¹ for now, "sensitive" means non-dumpable. This isn't perfect but it's
a reasonable approximation for now; it would be too expensive to do it
on *every* context switch. And for your purposes, the important part is
that it's what's upstream.
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WARNING: multiple messages have this Message-ID (diff)
From: "Woodhouse, David" <dwmw@amazon.co.uk>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Tim Chen <tim.c.chen@linux.intel.com>
Cc: <stable@vger.kernel.org>, Andy Lutomirski <luto@kernel.org>,
Nadav Amit <nadav.amit@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>,
Arjan van de Ven <arjan@linux.intel.com>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@intel.com>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
Mel Gorman <mgorman@suse.de>,
Peter Zijlstra <peterz@infradead.org>,
Rik van Riel <riel@redhat.com>, "Ingo Molnar" <mingo@kernel.org>,
<ak@linux.intel.com>, <karahmed@amazon.de>, <pbonzini@redhat.com>,
<linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/2] Backport IBPB on context switch to non-dumpable process
Date: Sat, 3 Mar 2018 12:37:55 +0100 [thread overview]
Message-ID: <1520077075.7929.4.camel@amazon.co.uk> (raw)
In-Reply-To: <20180303085454.GA23988@kroah.com>
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On Sat, 2018-03-03 at 09:54 +0100, Greg Kroah-Hartman wrote:
> On Fri, Mar 02, 2018 at 01:32:08PM -0800, Tim Chen wrote:
> >
> > Greg,
> >
> > I will like to propose backporting "x86/speculation: Use Indirect Branch
> > Prediction Barrier on context switch" from commit 18bf3c3e in upstream
> > to 4.9 and 4.4 stable. The patch has already been ported to 4.14 and
> > 4.15 stable. The patch needs mm context id that Andy added in commit
> > f39681ed. I have lifted the mm context id change from Andy's upstream
> > patch and included it here.
>
> What does this patch "fix" in those older kernels? Is this a
> performance improvement or something else?
It's part of the Spectre variant 2 mitigation — a full flush of the
branch prediction on context switch to a sensitive¹ process. It was the
one I called out as "needs more attention" when I did the rest of the
retpoline etc backportingk, and Tim has now fixed it up. (Thanks).
¹ for now, "sensitive" means non-dumpable. This isn't perfect but it's
a reasonable approximation for now; it would be too expensive to do it
on *every* context switch. And for your purposes, the important part is
that it's what's upstream.
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next prev parent reply other threads:[~2018-03-03 11:38 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-02 21:32 [PATCH 0/2] Backport IBPB on context switch to non-dumpable process Tim Chen
2018-03-02 21:32 ` Tim Chen
2018-03-02 21:32 ` [PATCH 1/2] x86/mm: Give each mm a unique ID Tim Chen
2018-03-02 21:32 ` Tim Chen
2018-03-07 17:30 ` Greg Kroah-Hartman
2018-03-07 17:30 ` Greg Kroah-Hartman
2018-03-08 18:23 ` Tim Chen
2018-03-10 1:04 ` Tim Chen
2018-03-10 1:14 ` Greg Kroah-Hartman
2018-03-02 21:32 ` [PATCH 2/2] x86/speculation: Use Indirect Branch Prediction Barrier in context switch Tim Chen
2018-03-02 21:32 ` Tim Chen
2018-03-02 21:32 ` Tim Chen
2018-03-03 8:54 ` [PATCH 0/2] Backport IBPB on context switch to non-dumpable process Greg Kroah-Hartman
2018-03-03 8:54 ` Greg Kroah-Hartman
2018-03-03 11:37 ` Woodhouse, David [this message]
2018-03-03 11:37 ` Woodhouse, David
2018-03-07 17:32 ` Greg Kroah-Hartman
2018-03-07 17:32 ` Greg Kroah-Hartman
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