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Re: [Xen-devel] [PATCH v6 2/4] x86/hvm: Treat non-instruction fetch nested page faults also as read violations
- To: Jan Beulich <JBeulich@xxxxxxxx>
- From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
- Date: Fri, 15 Aug 2014 20:17:07 +0000
- Accept-language: en-US
- Cc: "ian.campbell@xxxxxxxxxx" <ian.campbell@xxxxxxxxxx>, "stefano.stabellini@xxxxxxxxxxxxx" <stefano.stabellini@xxxxxxxxxxxxx>, "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>, AndrewCooper <andrew.cooper3@xxxxxxxxxx>, "ian.jackson@xxxxxxxxxxxxx" <ian.jackson@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxx>, "Dong, Eddie" <eddie.dong@xxxxxxxxx>, "Aravind.Gopalakrishnan@xxxxxxx" <Aravind.Gopalakrishnan@xxxxxxx>, "suravee.suthikulpanit@xxxxxxx" <suravee.suthikulpanit@xxxxxxx>, Tamas Lengyel <tamas.lengyel@xxxxxxxxxxxx>, "boris.ostrovsky@xxxxxxxxxx" <boris.ostrovsky@xxxxxxxxxx>
- Delivery-date: Fri, 15 Aug 2014 20:17:32 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
- Thread-index: AQHPtXN/h8RVUuy+3Uanc5w1EMyw6JvPQHcQ///6roCAARXEAIAAQ/ebgAAbkhD//4VoAIAAhlRw//98BQAAEOcfsP//gM2A//95DRCAAYg/gP//I8TQ
- Thread-topic: [Xen-devel] [PATCH v6 2/4] x86/hvm: Treat non-instruction fetch nested page faults also as read violations
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Friday, August 15, 2014 7:58 AM
>
> >>> On 15.08.14 at 01:40, <kevin.tian@xxxxxxxxx> wrote:
> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> >> The intended use is that pending patch I referred to, aiming at
> >> reducing the number of GLA->GPA translations we're doing during
> >> instruction emulation, which makes a severe difference to many-
> >> vCPU guests e.g. heavily using the HPET from all their vCPU-s.
> >
> > Is attached patch what you're talking here?
>
> Yes, that one.
>
Though I understand the merit of your overall patch, the discussion
around r/w violations are not directly related to the optimization
your patch brings (the real reason is from available GLA info at
VM-exit). It' just because you code the patch that way, so
__hvmemul_read purely assumes NPFEC_read_access if not is
NPFEC_insn_fetch, and then read-modify-write can't enter the
fast path w/o faking read.
If my understanding is correct, why not just do whatever tricks
here in nestedhvm_hap_nested_page_fault, while keeping arch
specific code unchanged?
Thanks
Kevin
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