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Re: [PATCH v2 4/4] x86/cpuid: Advertise SERIALIZE by default to guests
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 16 Dec 2021 17:48:43 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 16 Dec 2021 16:49:05 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 15.12.2021 23:21, Andrew Cooper wrote:
> I've played with SERIALIZE, TSXLDTRK, MOVDIRI and MOVDIR64 on real hardware,
> and they all seem fine, including emulation support.
>
> SERIALIZE exists specifically to have a userspace usable serialising operation
> without other side effects. (The only other two choices are CPUID which is a
> VMExit under virt and clobbers 4 registers, and IRET-to-self which very slow
> and consumes content from the stack.)
>
> TSXLDTRK is a niche TSX feature, and TSX itself is niche outside of demos of
> speculative sidechannels. Leave the feature opt-in until a usecase is found,
> in an effort to preempt the multiple person years of effort it has taken to
> mop up TSX issues impacting every processor line.
>
> MOVDIRI and MOVDIR64 are harder to judge. They're architectural building
> blocks towards ENQCMD{,S} without obvious usecases on their own. They're of
> no use to domains without PCI devices, so leave them opt-in for now.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
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