Andre Przywara
2011-Jan-26 14:04 UTC
[Xen-devel] [PATCH 2/2] hvm: allow pass-through of new CPUID features
Hi, there are some new CPUID features that are safe for guests to see, as they don''t require OS awareness (FPU/ALU related instructions only). Among features for new AMD CPUs there is also the PCLMULQDQ bit, which Intel CPU have already for quite a while. Signed-off-by: Andre Przywara <andre.przywara@amd.com> Regards, Andre. -- Andre Przywara AMD-Operating System Research Center (OSRC), Dresden, Germany _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Ian Jackson
2011-Jan-26 16:05 UTC
Re: [Xen-devel] [PATCH 2/2] hvm: allow pass-through of new CPUID features
Andre Przywara writes ("[Xen-devel] [PATCH 2/2] hvm: allow pass-through of
new CPUID features"):> there are some new CPUID features that are safe for guests to see, as
> they don''t require OS awareness (FPU/ALU related instructions
only).
> Among features for new AMD CPUs there is also the PCLMULQDQ bit, which
> Intel CPU have already for quite a while.
This would seem to be a new feature. We are currently in feature
freeze.
Can you make a justification for a freeze exception ?
Ian.
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Andre Przywara
2011-Jan-27 12:05 UTC
Re: [Xen-devel] [PATCH 2/2] hvm: allow pass-through of new CPUID features
Ian Jackson wrote:> Andre Przywara writes ("[Xen-devel] [PATCH 2/2] hvm: allow pass-through of new CPUID features"): >> there are some new CPUID features that are safe for guests to see, as >> they don''t require OS awareness (FPU/ALU related instructions only). >> Among features for new AMD CPUs there is also the PCLMULQDQ bit, which >> Intel CPU have already for quite a while. > > This would seem to be a new feature.I agree to some point, although (at least in respect to PCLMULQDQ) I''d consider this more as "forgotten enablement". > We are currently in feature freeze.> > Can you make a justification for a freeze exception ?If you can make me believe that it does not take another year until this shows up in an official release, then I am totally fine with skipping 4.1.0. What is the policy regarding the 4.1.x releases? Have features like those a chance of being applied? Regards, Andre. -- Andre Przywara AMD-Operating System Research Center (OSRC), Dresden, Germany _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Stefano Stabellini
2011-Jan-27 12:13 UTC
Re: [Xen-devel] [PATCH 2/2] hvm: allow pass-through of new CPUID features
On Thu, 27 Jan 2011, Andre Przywara wrote:> Ian Jackson wrote: > > Andre Przywara writes ("[Xen-devel] [PATCH 2/2] hvm: allow pass-through of new CPUID features"): > >> there are some new CPUID features that are safe for guests to see, as > >> they don''t require OS awareness (FPU/ALU related instructions only). > >> Among features for new AMD CPUs there is also the PCLMULQDQ bit, which > >> Intel CPU have already for quite a while. > > > > This would seem to be a new feature. > I agree to some point, although (at least in respect to PCLMULQDQ) I''d > consider this more as "forgotten enablement". > > > We are currently in feature freeze. > > > > Can you make a justification for a freeze exception ? > If you can make me believe that it does not take another year until this > shows up in an official release, then I am totally fine with skipping 4.1.0. > What is the policy regarding the 4.1.x releases? Have features like > those a chance of being applied?I think Ian was just looking for a well written explanation of why we need this now :) _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Ian Jackson
2011-Jan-27 14:53 UTC
Re: [Xen-devel] [PATCH 2/2] hvm: allow pass-through of new CPUID features
Stefano Stabellini writes ("Re: [Xen-devel] [PATCH 2/2] hvm: allow
pass-through of new CPUID features"):> I think Ian was just looking for a well written explanation of why we
> need this now :)
Yes, and particularly, a clear explanation of why applying this now
will not break things.
That would justify making an exception to the freeze with a clear
conscience :-).
Ian.
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Andre Przywara
2011-Jan-27 15:43 UTC
Re: [Xen-devel] [PATCH 2/2] hvm: allow pass-through of new CPUID features
Ian Jackson wrote:> Stefano Stabellini writes ("Re: [Xen-devel] [PATCH 2/2] hvm: allow pass-through of new CPUID features"): >> I think Ian was just looking for a well written explanation of why we >> need this now :)OK, I feel challenged, what about this: The new CPU features are pure "compute" features (ALU/FPU only), they don''t need any support or awareness from any system level software. Following the definition of virtualization they should be available to guests unless explicitly disabled. The AES feature was introduced at the same time as the PCLMULQDQ feature, AES is passed through, PCLMULQDQ has obviously been forgotten(?). The Linux kernel uses both instructions in newer versions for optimized cryptographic algorithms implementation (arch/x86/crypto/ghash-clmulni-intel_asm.S) The current version of the Xen hypervisor would deny this feature to any PV domains, including Dom0, leaving systems running under Xen with an inferior cryptographic performance. This patch allows PV domains to use the feature to get on par with systems running with other virtualization software. Regards, Andre. -- Andre Przywara AMD-Operating System Research Center (OSRC), Dresden, Germany _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Andre Przywara
2011-Jan-27 15:56 UTC
Re: [Xen-devel] [PATCH 2/2] hvm: allow pass-through of new CPUID features
Andre Przywara wrote:> Ian Jackson wrote: >> Stefano Stabellini writes ("Re: [Xen-devel] [PATCH 2/2] hvm: allow pass-through of new CPUID features"): >>> I think Ian was just looking for a well written explanation of why we >>> need this now :) > OK, I feel challenged, what about this: > > The new CPU features are pure "compute" features (ALU/FPU only), they > don''t need any support or awareness from any system level software. > Following the definition of virtualization they should be available to > guests unless explicitly disabled. > The AES feature was introduced at the same time as the PCLMULQDQ > feature, AES is passed through, PCLMULQDQ has obviously been forgotten(?). > The Linux kernel uses both instructions in newer versions for optimized > cryptographic algorithms implementation > (arch/x86/crypto/ghash-clmulni-intel_asm.S)> The current version of the Xen hypervisor would deny this feature to any > PV domains, including Dom0, leaving systems running under Xen with an > inferior cryptographic performance. > This patch allows PV domains to use the feature to get on par with > systems running with other virtualization software.Seems like I was a bit to eager with my rationale, this patch of course affects only HVM guests. Regards, Andre. -- Andre Przywara AMD-Operating System Research Center (OSRC), Dresden, Germany _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Keir Fraser
2011-Jan-27 16:07 UTC
Re: [Xen-devel] [PATCH 2/2] hvm: allow pass-through of new CPUID features
On 27/01/2011 15:43, "Andre Przywara" <andre.przywara@amd.com> wrote:> Ian Jackson wrote: >> Stefano Stabellini writes ("Re: [Xen-devel] [PATCH 2/2] hvm: allow >> pass-through of new CPUID features"): >>> I think Ian was just looking for a well written explanation of why we >>> need this now :) > OK, I feel challenged, what about this: > > The new CPU features are pure "compute" features (ALU/FPU only), they > don''t need any support or awareness from any system level software. > Following the definition of virtualization they should be available to > guests unless explicitly disabled. > The AES feature was introduced at the same time as the PCLMULQDQ > feature, AES is passed through, PCLMULQDQ has obviously been forgotten(?). > The Linux kernel uses both instructions in newer versions for optimized > cryptographic algorithms implementation > (arch/x86/crypto/ghash-clmulni-intel_asm.S) > The current version of the Xen hypervisor would deny this feature to any > PV domains, including Dom0, leaving systems running under Xen with an > inferior cryptographic performance. > This patch allows PV domains to use the feature to get on par with > systems running with other virtualization software.You''ve lost your mind a bit there. The patch affects only HVM guests. PV guests have a feature blacklist policy, and so these features are already passed through to PV guests (inc. dom0) just fine. -- Keir> Regards, > Andre. >_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Ian Jackson
2011-Jan-27 19:50 UTC
Re: [Xen-devel] [PATCH 2/2] hvm: allow pass-through of new CPUID features
Andre Przywara writes ("Re: [Xen-devel] [PATCH 2/2] hvm: allow pass-through
of new CPUID features"):> Andre Przywara wrote:
> > The new CPU features are pure "compute" features (ALU/FPU
only), they
> > don''t need any support or awareness from any system level
software.
> > Following the definition of virtualization they should be available to
> > guests unless explicitly disabled.
Thanks for that explanation. Can you confirm that these features
don''t involve new CPU state ? If so then I''m happy that they
should
go in despite the freeze.
Regards,
Ian.
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