From: Fenghua Yu <fenghua.yu@intel.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>,
"Luck, Tony" <tony.luck@intel.com>,
Dave Jiang <dave.jiang@intel.com>,
Ashok Raj <ashok.raj@intel.com>,
Ravi V Shankar <ravi.v.shankar@intel.com>,
Peter Zijlstra <peterz@infradead.org>, x86 <x86@kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
iommu@lists.linux-foundation.org, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>,
Jacob Jun Pan <jacob.jun.pan@intel.com>,
H Peter Anvin <hpa@zytor.com>,
Christoph Hellwig <hch@infradeed.org>,
Thomas Gleixner <tglx@linutronix.de>,
David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH v4 12/12] x86/traps: Fix up invalid PASID
Date: Fri, 26 Jun 2020 11:35:07 -0700 [thread overview]
Message-ID: <20200626183506.GB32961@romley-ivt3.sc.intel.com> (raw)
In-Reply-To: <aa3d7b7c-d6aa-06b4-30f7-0e90af50a1f3@intel.com>
Hi, Dave,
On Fri, Jun 26, 2020 at 11:23:12AM -0700, Dave Hansen wrote:
> On 6/26/20 11:10 AM, Luck, Tony wrote:
> > On Fri, Jun 26, 2020 at 11:44:50AM +0200, Peter Zijlstra wrote:
> >> On Thu, Jun 25, 2020 at 01:17:22PM -0700, Fenghua Yu wrote:
> >>
> >>> +static bool fixup_pasid_exception(void)
> >>> +{
> >>> + if (!IS_ENABLED(CONFIG_INTEL_IOMMU_SVM))
> >>> + return false;
> >>> + if (!static_cpu_has(X86_FEATURE_ENQCMD))
> >>> + return false;
> >>
> >> elsewhere you had another variation:
> >>
> >> + if (!IS_ENABLED(CONFIG_INTEL_IOMMU_SVM))
> >> + return;
> >> +
> >> + if (!cpu_feature_enabled(X86_FEATURE_ENQCMD))
> >> + return;
> >>
> >> Which is it, and why do we need the CONFIG thing when combined with the
> >> enabled thing?
> >
> > Do we have a standard way of coding for a feature that depends on multiple
> > other features? For this case the system needs to both suport the ENQCMD
> > instruction, and also have kernel code that programs the IOMMU.
>
> Not really a standard one.
>
> We could setup_clear_cpu_cap(X86_FEATURE_ENQCMD) during boot if we see
> that CONFIG_INTEL_IOMMU_SVM=n or if we don't have a detected IOMMU.
> That would at least get static value patching which would make some of
> the feature checks very cheap.
>
> That means we can't use ENQCMD at all in the kernel, though. Is that an
> issue? Is the CPU feature truly dependent on IOMMU_SVM?
ENQCMD instruction needs bind_mm()/unbind_mm() defined in svm.c
which is only compiled by:
obj-$(CONFIG_INTEL_IOMMU_SVM) += intel/svm.o
So I think ENQCMD instruction is truly dependent on CONFIG_INTEL_IOMMU_SVM.
>
> > And/or guidance on when to use each of the very somewhat simlar looking
> > boot_cpu_has()
> > static_cpu_has()
> > IS_ENABLED()
> > cpu_feature_enabled(X86_FEATURE_ENQCMD)
> > options?
>
> cpu_feature_enabled() is by go-to for checking X86_FEATUREs. It has
> compile-time checking along with static checking.
>
> If you use cpu_feature_enabled(), and we added:
>
> #ifdef CONFIG_INTEL_IOMMU_SVM
> # define DISABLE_ENQCMD 0
> #else
> # define DISABLE_ENQCMD (1 << (X86_FEATURE_ENQCMD & <bitval>))
> #endif
>
> to arch/x86/include/asm/disabled-features.h, then we could check only
> X86_FEATURE_ENQCMD, and we'd get that IS_ENABLED() check for "free".
This makes code simpler and cleaner.
Thanks.
-Fenghua
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next prev parent reply other threads:[~2020-06-26 18:35 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-25 20:17 [PATCH v4 00/12] x86: tag application address space for devices Fenghua Yu
2020-06-25 20:17 ` [PATCH v4 01/12] iommu: Change type of pasid to u32 Fenghua Yu
2020-06-26 1:13 ` Lu Baolu
2020-06-25 20:17 ` [PATCH v4 02/12] iommu/vt-d: Change flags type to unsigned int in binding mm Fenghua Yu
2020-06-26 1:14 ` Lu Baolu
2020-06-25 20:17 ` [PATCH v4 03/12] docs: x86: Add documentation for SVA (Shared Virtual Addressing) Fenghua Yu
2020-06-25 20:17 ` [PATCH v4 04/12] x86/cpufeatures: Enumerate ENQCMD and ENQCMDS instructions Fenghua Yu
2020-06-25 20:17 ` [PATCH v4 05/12] x86/fpu/xstate: Add supervisor PASID state for ENQCMD feature Fenghua Yu
2020-06-25 20:17 ` [PATCH v4 06/12] x86/msr-index: Define IA32_PASID MSR Fenghua Yu
2020-06-25 20:17 ` [PATCH v4 07/12] mm: Define pasid in mm Fenghua Yu
2020-06-25 20:17 ` [PATCH v4 08/12] fork: Clear PASID for new mm Fenghua Yu
2020-06-25 20:17 ` [PATCH v4 09/12] x86/process: Clear PASID state for a newly forked/cloned thread Fenghua Yu
2020-06-25 20:17 ` [PATCH v4 10/12] x86/mmu: Allocate/free PASID Fenghua Yu
2020-06-26 1:42 ` Lu Baolu
2020-06-25 20:17 ` [PATCH v4 11/12] sched: Define and initialize a flag to identify valid PASID in the task Fenghua Yu
2020-06-25 20:17 ` [PATCH v4 12/12] x86/traps: Fix up invalid PASID Fenghua Yu
2020-06-26 1:46 ` Lu Baolu
2020-06-26 9:44 ` Peter Zijlstra
2020-06-26 18:10 ` Luck, Tony
2020-06-26 18:15 ` Borislav Petkov
2020-06-26 18:23 ` Dave Hansen
2020-06-26 18:35 ` Fenghua Yu [this message]
2020-06-26 18:16 ` Fenghua Yu
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