Re: [PATCH v2 00/12] x86: tag application address space for devices

From: Fenghua Yu <fenghua.yu@intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@intel.com>,
	H Peter Anvin <hpa@zytor.com>, Dave Jiang <dave.jiang@intel.com>,
	Ashok Raj <ashok.raj@intel.com>, x86 <x86@kernel.org>,
	amd-gfx <amd-gfx@lists.freedesktop.org>,
	Ingo Molnar <mingo@redhat.com>,
	Ravi V Shankar <ravi.v.shankar@intel.com>,
	Yu-cheng Yu <yu-cheng.yu@intel.com>,
	Andrew Donnellan <ajd@linux.ibm.com>,
	Borislav Petkov <bp@alien8.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Tony Luck <tony.luck@intel.com>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	Felix Kuehling <Felix.Kuehling@amd.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	iommu@lists.linux-foundation.org,
	Jacob Jun Pan <jacob.jun.pan@intel.com>,
	Frederic Barrat <fbarrat@linux.ibm.com>,
	David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH v2 00/12] x86: tag application address space for devices
Date: Mon, 15 Jun 2020 07:53:46 -0700	[thread overview]
Message-ID: <20200615145345.GA13792@romley-ivt3.sc.intel.com> (raw)
In-Reply-To: <20200615075202.GI2497@hirez.programming.kicks-ass.net>

Hi, Peter,
On Mon, Jun 15, 2020 at 09:52:02AM +0200, Peter Zijlstra wrote:
> On Fri, Jun 12, 2020 at 05:41:21PM -0700, Fenghua Yu wrote:
> 
> > This series only provides simple and basic support for ENQCMD and the MSR:
> > 1. Clean up type definitions (patch 1-3). These patches can be in a
> >    separate series.
> >    - Define "pasid" as "unsigned int" consistently (patch 1 and 2).
> >    - Define "flags" as "unsigned int"
> > 2. Explain different various technical terms used in the series (patch 4).
> > 3. Enumerate support for ENQCMD in the processor (patch 5).
> > 4. Handle FPU PASID state and the MSR during context switch (patches 6-7).
> > 5. Define "pasid" in mm_struct (patch 8).
> > 5. Clear PASID state for new mm and forked and cloned thread (patch 9-10).
> > 6. Allocate and free PASID for a process (patch 11).
> > 7. Fix up the PASID MSR in #GP handler when one thread in a process
> >    executes ENQCMD for the first time (patches 12).
> 
> If this is per mm, should not switch_mm() update the MSR ? I'm not
> seeing that, nor do I see it explained why not.

PASID value is per mm and all threads in a process have the same PASID
value in the MSR. However, the MSR is per thread and is context switched
by XSAVES/XRSTROS in patches 6-7.

Thanks.

-Fenghua
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