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Re: [Xen-devel] [PATCH] x86/svm: Reduce vmentry latency

To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

From: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Date: Mon, 10 Feb 2020 13:09:56 +0100

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Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>

Delivery-date: Mon, 10 Feb 2020 12:10:17 +0000

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List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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@xxxxxxxxxx> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx> Thanks. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel

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