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From: Dave Hansen <dave.hansen@intel.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: Ravi V Shankar <ravi.v.shankar@intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	H Peter Anvin <hpa@zytor.com>,
	Jean-Philippe Brucker <jean-philippe@linaro.org>,
	Dave Jiang <dave.jiang@intel.com>,
	Ashok Raj <ashok.raj@intel.com>, Joerg Roedel <joro@8bytes.org>,
	x86 <x86@kernel.org>, amd-gfx <amd-gfx@lists.freedesktop.org>,
	Christoph Hellwig <hch@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, Fenghua Yu <fenghua.yu@intel.com>,
	Borislav Petkov <bp@alien8.de>,
	Sohil Mehta <sohil.mehta@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Tony Luck <tony.luck@intel.com>,
	Felix Kuehling <Felix.Kuehling@amd.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	iommu <iommu@lists.linux-foundation.org>,
	Jacob Jun Pan <jacob.jun.pan@intel.com>,
	David Woodhouse <dwmw2@infradead.org>,
	Lu Baolu <baolu.lu@linux.intel.com>
Subject: Re: [PATCH v6 12/12] x86/traps: Fix up invalid PASID
Date: Mon, 3 Aug 2020 09:36:55 -0700
Message-ID: <12fbdc01-e444-8d10-5790-e3495fc8a837@intel.com> (raw)
In-Reply-To: <CALCETrXLFwzCzoE8ZjciBO_WSK8StyTfO1yXVm4v2qFQZpfasg@mail.gmail.com>

On 8/3/20 8:12 AM, Andy Lutomirski wrote:
> I could easily be convinced that the PASID fixup is so trivial and so
> obviously free of misfiring in a way that causes an infinite loop that
> this code is fine.  But I think we first need to answer the bigger
> question of why we're doing a lazy fixup in the first place.

There was an (internal to Intel) implementation of this about a year ago
that used smp_call_function_many() to force the MSR state into all
threads of a process.  I took one look at it, decided there was a 0%
chance of it actually functioning and recommended we find another way.
While I'm sure it could be done more efficiently, the implementation I
looked at took ~200 lines of code and comments.  It started to look too
much like another instance of mm->cpumask for my comfort.

The only other option I could think of would be an ABI where threads
were required to call into the kernel at least once after creation
before calling ENQCMD.  All ENQCMDs would be required to be "wrapped" by
code doing this syscall.  Something like this:

	if (!thread_local(did_pasid_init))
		sys_pasid_init(); // new syscall or prctl

	thread_local(did_pasid_init) = 1;

	// ENQCMD here
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  parent reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-13 23:47 [PATCH v6 00/12] x86: tag application address space for devices Fenghua Yu
2020-07-13 23:47 ` [PATCH v6 01/12] iommu: Change type of pasid to u32 Fenghua Yu
2020-07-14  2:45   ` Liu, Yi L
2020-07-14 13:54     ` Fenghua Yu
2020-07-14 13:56       ` Liu, Yi L
2020-07-22 14:03   ` Joerg Roedel
2020-07-22 17:21     ` Fenghua Yu
2020-07-13 23:47 ` [PATCH v6 02/12] iommu/vt-d: Change flags type to unsigned int in binding mm Fenghua Yu
2020-07-13 23:47 ` [PATCH v6 03/12] docs: x86: Add documentation for SVA (Shared Virtual Addressing) Fenghua Yu
2020-07-14  3:25   ` Liu, Yi L
2020-07-15 23:32     ` Fenghua Yu
2020-07-13 23:47 ` [PATCH v6 04/12] x86/cpufeatures: Enumerate ENQCMD and ENQCMDS instructions Fenghua Yu
2020-07-13 23:48 ` [PATCH v6 05/12] x86/fpu/xstate: Add supervisor PASID state for ENQCMD feature Fenghua Yu
2020-07-13 23:48 ` [PATCH v6 06/12] x86/msr-index: Define IA32_PASID MSR Fenghua Yu
2020-07-13 23:48 ` [PATCH v6 07/12] mm: Define pasid in mm Fenghua Yu
2020-07-13 23:48 ` [PATCH v6 08/12] fork: Clear PASID for new mm Fenghua Yu
2020-07-13 23:48 ` [PATCH v6 09/12] x86/process: Clear PASID state for a newly forked/cloned thread Fenghua Yu
2020-08-01  1:44   ` Andy Lutomirski
2020-07-13 23:48 ` [PATCH v6 10/12] x86/mmu: Allocate/free PASID Fenghua Yu
2020-07-13 23:48 ` [PATCH v6 11/12] sched: Define and initialize a flag to identify valid PASID in the task Fenghua Yu
2020-07-13 23:48 ` [PATCH v6 12/12] x86/traps: Fix up invalid PASID Fenghua Yu
2020-07-31 23:34   ` Andy Lutomirski
2020-08-01  0:42     ` Fenghua Yu
2020-08-03 15:03     ` Dave Hansen
2020-08-03 15:12       ` Andy Lutomirski
2020-08-03 15:19         ` Raj, Ashok
2020-08-03 16:36         ` Dave Hansen [this message]
2020-08-03 17:16           ` Andy Lutomirski
2020-08-03 17:34             ` Dave Hansen
2020-08-03 19:24               ` Andy Lutomirski
2020-08-01  1:28   ` Andy Lutomirski
2020-08-03 17:19     ` Fenghua Yu

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