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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: "Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Arnaldo Carvalho de Melo" <acme@kernel.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Alexander Shishkin" <alexander.shishkin@linux.intel.com>,
	"Jiri Olsa" <jolsa@redhat.com>,
	"Namhyung Kim" <namhyung@kernel.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Vitaly Kuznetsov" <vkuznets@redhat.com>,
	"Wanpeng Li" <wanpengli@tencent.com>,
	"Jim Mattson" <jmattson@google.com>,
	"Joerg Roedel" <joro@8bytes.org>,
	"Tony Luck" <tony.luck@intel.com>,
	"Tony W Wang-oc" <TonyWWang-oc@zhaoxin.com>,
	"Shuah Khan" <shuah@kernel.org>,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	linux-edac@vger.kernel.org, linux-kselftest@vger.kernel.org,
	"Jarkko Sakkinen" <jarkko.sakkinen@linux.intel.com>
Subject: Re: [PATCH v3 12/19] x86/vmx: Introduce VMX_FEATURES_*
Date: Fri, 22 Nov 2019 11:09:27 -0800
Message-ID: <20191122190927.GB31235@linux.intel.com> (raw)
In-Reply-To: <20191122183641.GJ6289@zn.tnic>

On Fri, Nov 22, 2019 at 07:36:41PM +0100, Borislav Petkov wrote:
> On Thu, Nov 21, 2019 at 01:50:17PM -0800, Sean Christopherson wrote:
> > As for why I want to keep these out of cpu_has()... VMX has a concept of
> > features being fixed "on", e.g. early CPUs don't allow disabling off CR3
> > interception.  A cpu_has() approach doesn't work well since it loses the
> > information regarding which bits are fixed-1.  KVM also has several module
> > params that can be used to disable use of features, i.e. we don't want
> > cpu_has() for VMX features because the KVM-specific variables need to be
> > the canonical reference.
> 
> Well, you can use the cpu_has() machinery for stuff like that too - we
> can clear bits there too: clear_cpu_cap() - and since clearing those
> bits are only for /proc/cpuinfo reporting, it's not like anything would
> break if that flag is gone. Just saying, in case you want to use the
> machinery for that.

It doesn't fit the KVM use case very well.  There is an obnoxious amount
of legacy KVM code that exists only to support old processors (10+ years
old), but that we can't get rid of because people are still actively
running KVM on old hardware.  KVM provides module params so that we can
easily test those flows on modern hardware, e.g. for certain changes I'll
reload and retest KVM 2-3 times with different settings.

In theory we could do something like recompute VMX_FEATURE_* when KVM is
loaded, but that'd be a bit ugly and there are also tenative plans to move
the relevant module params under an ioctl() so that they can be toggled on
a per-VM basis to help automate testing, and IIRC for customers running
certain legacy workloads alongside normal VMs

> And that would avoid some of the duplication of having KVM-specific
> variables *and* VMX_FEATURE_* flags, where latter are not really
> toggleable but only for /proc/cpuinfo. Especially if you wanna enforce
> "developers to define a VMX_FEATURE flag when adding support for a new
> hardware feature."

  reply index

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-19  3:12 [PATCH v3 00/19] x86/cpu: Clean up handling of VMX features Sean Christopherson
2019-11-19  3:12 ` [PATCH v3 01/19] x86/msr-index: Clean up bit defines for IA32_FEATURE_CONTROL MSR Sean Christopherson
2019-11-19 11:15   ` Borislav Petkov
2019-11-19 23:18     ` Sean Christopherson
2019-11-20 17:48       ` Borislav Petkov
2019-11-21  9:46   ` Jarkko Sakkinen
2019-11-21 22:14     ` Sean Christopherson
2019-11-29 21:06       ` Jarkko Sakkinen
2019-11-29 21:11         ` Jarkko Sakkinen
2019-11-19  3:12 ` [PATCH v3 02/19] selftests: kvm: Replace manual MSR defs with common msr-index.h Sean Christopherson
2019-11-19  3:12 ` [PATCH v3 03/19] tools arch x86: Sync msr-index.h from kernel sources Sean Christopherson
2019-11-19  3:12 ` [PATCH v3 04/19] x86/intel: Initialize IA32_FEATURE_CONTROL MSR at boot Sean Christopherson
2019-11-19  4:41   ` Kai Huang
2019-11-19  5:03     ` Sean Christopherson
2019-11-21 10:39   ` Jarkko Sakkinen
2019-11-21 10:41     ` Jarkko Sakkinen
2019-11-21 11:05       ` Borislav Petkov
2019-11-21 22:12         ` Sean Christopherson
2019-11-22 12:34           ` Borislav Petkov
2019-11-19  3:12 ` [PATCH v3 05/19] x86/mce: WARN once if IA32_FEATURE_CONTROL MSR is left unlocked Sean Christopherson
2019-11-21 10:45   ` Jarkko Sakkinen
2019-11-19  3:12 ` [PATCH v3 06/19] x86/centaur: Use common IA32_FEATURE_CONTROL MSR initialization Sean Christopherson
2019-11-19  3:12 ` [PATCH v3 07/19] x86/zhaoxin: " Sean Christopherson
2019-11-19  3:12 ` [PATCH v3 08/19] KVM: VMX: Drop initialization of IA32_FEATURE_CONTROL MSR Sean Christopherson
2019-11-19  3:12 ` [PATCH v3 09/19] x86/cpu: Clear VMX feature flag if VMX is not fully enabled Sean Christopherson
2019-11-21 16:24   ` Borislav Petkov
2019-11-21 21:07     ` Sean Christopherson
2019-11-22 16:02       ` Borislav Petkov
2019-11-19  3:12 ` [PATCH v3 10/19] KVM: VMX: Use VMX feature flag to query BIOS enabling Sean Christopherson
2019-11-19  3:12 ` [PATCH v3 11/19] KVM: VMX: Check for full VMX support when verifying CPU compatibility Sean Christopherson
2019-11-19  3:12 ` [PATCH v3 12/19] x86/vmx: Introduce VMX_FEATURES_* Sean Christopherson
2019-11-21 16:52   ` Borislav Petkov
2019-11-21 21:50     ` Sean Christopherson
2019-11-22 18:36       ` Borislav Petkov
2019-11-22 19:09         ` Sean Christopherson [this message]
2019-11-19  3:12 ` [PATCH v3 13/19] x86/cpu: Detect VMX features on Intel, Centaur and Zhaoxin CPUs Sean Christopherson
2019-11-19  3:12 ` [PATCH v3 14/19] x86/cpu: Print VMX flags in /proc/cpuinfo using VMX_FEATURES_* Sean Christopherson
2019-11-19  3:12 ` [PATCH v3 15/19] x86/cpufeatures: Drop synthetic VMX feature flags Sean Christopherson
2019-11-19  3:12 ` [PATCH v3 16/19] KVM: VMX: Use VMX_FEATURE_* flags to define VMCS control bits Sean Christopherson
2019-11-19  3:12 ` [PATCH v3 17/19] x86/cpufeatures: Clean up synthetic virtualization flags Sean Christopherson
2019-11-19  3:12 ` [PATCH v3 18/19] perf/x86: Provide stubs of KVM helpers for non-Intel CPUs Sean Christopherson
2019-11-19  3:12 ` [PATCH v3 19/19] KVM: VMX: Allow KVM_INTEL when building for Centaur and/or Zhaoxin CPUs Sean Christopherson

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