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From: "Jacob Pan (Jun)" <jacob.jun.pan@intel.com>
To: "Luck, Tony" <tony.luck@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	"Yu, Fenghua" <fenghua.yu@intel.com>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	H Peter Anvin <hpa@zytor.com>,
	David Woodhouse <dwmw2@infradead.org>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	"Raj, Ashok" <ashok.raj@intel.com>,
	"Jiang, Dave" <dave.jiang@intel.com>,
	"Mehta, Sohil" <sohil.mehta@intel.com>,
	"Shankar, Ravi V" <ravi.v.shankar@intel.com>,
	linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	jacob.jun.pan@intel.com
Subject: Re: [PATCH 5/7] x86/mmu: Allocate/free PASID
Date: Tue, 28 Apr 2020 15:13:03 -0700	[thread overview]
Message-ID: <20200428151303.00004fa2@intel.com> (raw)
In-Reply-To: <3908561D78D1C84285E8C5FCA982C28F7F608EE2@ORSMSX115.amr.corp.intel.com>

On Tue, 28 Apr 2020 13:59:43 -0700
"Luck, Tony" <tony.luck@intel.com> wrote:

> >> So the driver needs to use flush/drain operations to make sure all
> >> the in-flight work has completed before releasing/re-using the
> >> PASID. 
> > Are you suggesting we should let driver also hold a reference of the
> > PASID?  
> 
> The sequence for bare metal is:
> 
> 	process is queuing requests to DSA
> 	process exits (either deliberately, or crashes, or is killed)
> 	kernel does exit processing
> 	DSA driver is called as part of tear down of "mm"
> 		issues drain/flush commands to ensure that all
> 		queued operations on the PASID for this mm have
> 		completed
> 	PASID can be freed
> 
> There's a 1:1 map from "mm" to PASID ... so reference counting seems
> like overkill. Once the kernel is in the "exit" path, we know that no
> more work can be queued using this PASID.
> 
There are two users of a PASID, mm and device driver(FD). If
either one is not done with the PASID, it cannot be reclaimed. As you
mentioned, it could take a long time for the driver to abort. If the
abort ends *after* mmdrop, we are in trouble.
If driver drops reference after abort/drain PASID is done, then we are
safe.


> -Tony


  reply	other threads:[~2020-04-28 22:13 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-30 19:33 [PATCH 0/7] x86: tag application address space for devices Fenghua Yu
2020-03-30 19:33 ` [PATCH 1/7] docs: x86: Add a documentation for ENQCMD Fenghua Yu
2020-04-26 11:02   ` Thomas Gleixner
2020-04-27 20:13     ` Fenghua Yu
2020-03-30 19:33 ` [PATCH 2/7] x86/cpufeatures: Enumerate ENQCMD and ENQCMDS instructions Fenghua Yu
2020-04-26 11:06   ` Thomas Gleixner
2020-04-27 20:17     ` Fenghua Yu
2020-03-30 19:33 ` [PATCH 3/7] x86/fpu/xstate: Add supervisor PASID state for ENQCMD feature Fenghua Yu
2020-04-26 11:17   ` Thomas Gleixner
2020-04-27 20:33     ` Fenghua Yu
2020-03-30 19:33 ` [PATCH 4/7] x86/msr-index: Define IA32_PASID MSR Fenghua Yu
2020-04-26 11:22   ` Thomas Gleixner
2020-04-27 20:50     ` Fenghua Yu
2020-03-30 19:33 ` [PATCH 5/7] x86/mmu: Allocate/free PASID Fenghua Yu
2020-04-26 14:55   ` Thomas Gleixner
2020-04-27 22:18     ` Fenghua Yu
2020-04-27 23:44       ` Thomas Gleixner
2020-04-28 18:21     ` Jacob Pan (Jun)
2020-04-28 18:54       ` Thomas Gleixner
2020-04-28 19:07         ` Luck, Tony
2020-04-28 20:42           ` Jacob Pan (Jun)
2020-04-28 20:59             ` Luck, Tony
2020-04-28 22:13               ` Jacob Pan (Jun) [this message]
2020-04-28 22:32                 ` Luck, Tony
2020-04-28 20:40         ` Jacob Pan (Jun)
2020-04-28 20:57     ` Fenghua Yu
2020-03-30 19:33 ` [PATCH 6/7] x86/traps: Fix up invalid PASID Fenghua Yu
2020-04-26 15:25   ` Thomas Gleixner
2020-04-27 20:11     ` Fenghua Yu
2020-04-28  0:13       ` Thomas Gleixner
2020-04-27 22:46     ` Raj, Ashok
2020-04-27 23:08       ` Luck, Tony
2020-04-28  0:20         ` Thomas Gleixner
2020-04-28  0:54       ` Thomas Gleixner
2020-04-28  1:08         ` Raj, Ashok
2020-03-30 19:33 ` [PATCH 7/7] x86/process: Clear PASID state for a newly forked/cloned thread Fenghua Yu
2020-04-22 20:41 ` [PATCH 0/7] x86: tag application address space for devices Fenghua Yu

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