All of lore.kernel.org
 help / color / mirror / Atom feed
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


WARNING: multiple messages have this Message-ID (diff)
From: "Jacob Pan (Jun)" <jacob.jun.pan@intel.com>
To: "Luck, Tony" <tony.luck@intel.com>
Cc: "Yu, Fenghua" <fenghua.yu@intel.com>,
	"Jiang, Dave" <dave.jiang@intel.com>,
	"Raj, Ashok" <ashok.raj@intel.com>,
	"Shankar,  Ravi V" <ravi.v.shankar@intel.com>,
	x86 <x86@kernel.org>, linux-kernel <linux-kernel@vger.kernel.org>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	jacob.jun.pan@intel.com, H Peter Anvin <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	David Woodhouse <dwmw2@infradead.org>
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

_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu

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

Thread overview: 74+ 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 ` Fenghua Yu
2020-03-30 19:33 ` [PATCH 1/7] docs: x86: Add a documentation for ENQCMD Fenghua Yu
2020-03-30 19:33   ` Fenghua Yu
2020-04-26 11:02   ` Thomas Gleixner
2020-04-26 11:02     ` Thomas Gleixner
2020-04-27 20:13     ` Fenghua Yu
2020-04-27 20:13       ` Fenghua Yu
2020-03-30 19:33 ` [PATCH 2/7] x86/cpufeatures: Enumerate ENQCMD and ENQCMDS instructions Fenghua Yu
2020-03-30 19:33   ` Fenghua Yu
2020-04-26 11:06   ` Thomas Gleixner
2020-04-26 11:06     ` Thomas Gleixner
2020-04-27 20:17     ` Fenghua Yu
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
2020-03-30 19:33   ` Fenghua Yu
2020-04-26 11:17   ` Thomas Gleixner
2020-04-26 11:17     ` Thomas Gleixner
2020-04-27 20:33     ` Fenghua Yu
2020-04-27 20:33       ` Fenghua Yu
2020-03-30 19:33 ` [PATCH 4/7] x86/msr-index: Define IA32_PASID MSR Fenghua Yu
2020-03-30 19:33   ` Fenghua Yu
2020-04-26 11:22   ` Thomas Gleixner
2020-04-26 11:22     ` Thomas Gleixner
2020-04-27 20:50     ` Fenghua Yu
2020-04-27 20:50       ` Fenghua Yu
2020-03-30 19:33 ` [PATCH 5/7] x86/mmu: Allocate/free PASID Fenghua Yu
2020-03-30 19:33   ` Fenghua Yu
2020-04-26 14:55   ` Thomas Gleixner
2020-04-26 14:55     ` Thomas Gleixner
2020-04-27 22:18     ` Fenghua Yu
2020-04-27 22:18       ` Fenghua Yu
2020-04-27 23:44       ` Thomas Gleixner
2020-04-27 23:44         ` Thomas Gleixner
2020-04-28 18:21     ` Jacob Pan (Jun)
2020-04-28 18:21       ` Jacob Pan (Jun)
2020-04-28 18:54       ` Thomas Gleixner
2020-04-28 18:54         ` Thomas Gleixner
2020-04-28 19:07         ` Luck, Tony
2020-04-28 19:07           ` Luck, Tony
2020-04-28 20:42           ` Jacob Pan (Jun)
2020-04-28 20:42             ` Jacob Pan (Jun)
2020-04-28 20:59             ` Luck, Tony
2020-04-28 20:59               ` Luck, Tony
2020-04-28 22:13               ` Jacob Pan (Jun) [this message]
2020-04-28 22:13                 ` Jacob Pan (Jun)
2020-04-28 22:32                 ` Luck, Tony
2020-04-28 22:32                   ` Luck, Tony
2020-04-28 20:40         ` Jacob Pan (Jun)
2020-04-28 20:40           ` Jacob Pan (Jun)
2020-04-28 20:57     ` Fenghua Yu
2020-04-28 20:57       ` Fenghua Yu
2020-03-30 19:33 ` [PATCH 6/7] x86/traps: Fix up invalid PASID Fenghua Yu
2020-03-30 19:33   ` Fenghua Yu
2020-04-26 15:25   ` Thomas Gleixner
2020-04-26 15:25     ` Thomas Gleixner
2020-04-27 20:11     ` Fenghua Yu
2020-04-27 20:11       ` Fenghua Yu
2020-04-28  0:13       ` Thomas Gleixner
2020-04-28  0:13         ` Thomas Gleixner
2020-04-27 22:46     ` Raj, Ashok
2020-04-27 22:46       ` Raj, Ashok
2020-04-27 23:08       ` Luck, Tony
2020-04-27 23:08         ` Luck, Tony
2020-04-28  0:20         ` Thomas Gleixner
2020-04-28  0:20           ` Thomas Gleixner
2020-04-28  0:54       ` Thomas Gleixner
2020-04-28  0:54         ` Thomas Gleixner
2020-04-28  1:08         ` Raj, Ashok
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
2020-03-30 19:33   ` Fenghua Yu
2020-04-22 20:41 ` [PATCH 0/7] x86: tag application address space for devices Fenghua Yu
2020-04-22 20:41   ` Fenghua Yu

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200428151303.00004fa2@intel.com \
    --to=jacob.jun.pan@intel.com \
    --cc=ashok.raj@intel.com \
    --cc=baolu.lu@linux.intel.com \
    --cc=bp@alien8.de \
    --cc=dave.hansen@intel.com \
    --cc=dave.jiang@intel.com \
    --cc=dwmw2@infradead.org \
    --cc=fenghua.yu@intel.com \
    --cc=hpa@zytor.com \
    --cc=iommu@lists.linux-foundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=ravi.v.shankar@intel.com \
    --cc=sohil.mehta@intel.com \
    --cc=tglx@linutronix.de \
    --cc=tony.luck@intel.com \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.