From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Xen-devel <xen-devel@lists.xenproject.org>, Wei Liu <wl@xen.org>,
Jan Beulich <JBeulich@suse.com>
Subject: Re: [Xen-devel] [PATCH] x86/svm: Reduce vmentry latency
Date: Mon, 10 Feb 2020 13:09:56 +0100 [thread overview]
Message-ID: <20200210120956.GH4679@Air-de-Roger> (raw)
In-Reply-To: <20200210114206.17115-1-andrew.cooper3@citrix.com>
On Mon, Feb 10, 2020 at 11:42:06AM +0000, Andrew Cooper wrote:
> Writing to the stack pointer in the middle of a line of pop operations is
> specifically recommended against by the optimisation guide, and is a technique
> used by Speculative Load Hardening to combat SpectreRSB.
>
> In practice, it causes all further stack-relative accesses to block until the
> write to the stack pointer retires, so the stack engine can get back in sync.
>
> Pop into any dead register to discard %rax's value without clobbering the
> stack engine. Smaller compiled code, and runs faster.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Thanks.
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next prev parent reply other threads:[~2020-02-10 12:10 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-10 11:42 [Xen-devel] [PATCH] x86/svm: Reduce vmentry latency Andrew Cooper
2020-02-10 12:09 ` Roger Pau Monné [this message]
2020-02-10 16:52 ` Jan Beulich
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