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From: Fenghua Yu <fenghua.yu@intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	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>,
	Frederic Barrat <fbarrat@linux.ibm.com>,
	Andrew Donnellan <ajd@linux.ibm.com>,
	Felix Kuehling <Felix.Kuehling@amd.com>,
	Joerg Roedel <joro@8bytes.org>,
	Dave Hansen <dave.hansen@intel.com>,
	Tony Luck <tony.luck@intel.com>, Ashok Raj <ashok.raj@intel.com>,
	Jacob Jun Pan <jacob.jun.pan@intel.com>,
	Dave Jiang <dave.jiang@intel.com>,
	Yu-cheng Yu <yu-cheng.yu@intel.com>,
	Sohil Mehta <sohil.mehta@intel.com>,
	Ravi V Shankar <ravi.v.shankar@intel.com>,
	linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>,
	iommu@lists.linux-foundation.org,
	amd-gfx <amd-gfx@lists.freedesktop.org>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID
Date: Mon, 15 Jun 2020 11:55:29 -0700	[thread overview]
Message-ID: <20200615185529.GD13792@romley-ivt3.sc.intel.com> (raw)
In-Reply-To: <20200615183116.GD2531@hirez.programming.kicks-ass.net>

Hi, Peter,

On Mon, Jun 15, 2020 at 08:31:16PM +0200, Peter Zijlstra wrote:
> On Mon, Jun 15, 2020 at 11:12:59AM -0700, Fenghua Yu wrote:
> > > I don't get why you need a rdmsr here, or why not having one would
> > > require a TIF flag. Is that because this MSR is XSAVE/XRSTOR managed?
> > 
> > My concern is TIF flags are precious (only 3 slots available). Defining
> > a new TIF flag may be not worth it while rdmsr() can check if PASID
> > is valid in the MSR. And performance here might not be a big issue
> > in #GP.
> > 
> > But if you think using TIF flag is better, I can define a new TIF flag
> > and maintain it per thread (init 0 when clone()/fork(), set 1 in fixup()).
> > Then we can avoid using rdmsr() to check valid PASID in the MSR.
> 
> WHY ?!?! What do you need a TIF flag for?

We need "a way" to check if the per thread MSR has a valid PASID. If yes,
no need to fix up the MSR (wrmsr()), and let other handler to handle the #GP.
Otherwise, apply the heuristics and fix up the MSR and exit the #GP.

The way to check the valid PASID in the MSR is rdmsr() in this series.
A TIF flag will be much faster than rdmsr() and seems a sutiable way
to check valid PASID status per thread. That's why it could replace
rdmsr() to check PASID in the MSR.

Or do you suggest to add a random new flag in struct thread_info instead
of a TIF flag?

Thanks.

-Fenghua


  reply	other threads:[~2020-06-15 18:55 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-13  0:41 [PATCH v2 00/12] x86: tag application address space for devices Fenghua Yu
2020-06-13  0:41 ` [PATCH v2 01/12] iommu: Change type of pasid to unsigned int Fenghua Yu
2020-06-13  0:41 ` [PATCH v2 02/12] ocxl: " Fenghua Yu
2020-06-18  8:05   ` Frederic Barrat
2020-06-18 15:37     ` Fenghua Yu
2020-06-18 16:56       ` Frederic Barrat
2020-06-13  0:41 ` [PATCH v2 03/12] iommu/vt-d: Change flags type to unsigned int in binding mm Fenghua Yu
2020-06-13  0:41 ` [PATCH v2 04/12] docs: x86: Add documentation for SVA (Shared Virtual Addressing) Fenghua Yu
2020-06-13 12:17   ` Lu Baolu
2020-06-15 23:16     ` Fenghua Yu
2020-06-13  0:41 ` [PATCH v2 05/12] x86/cpufeatures: Enumerate ENQCMD and ENQCMDS instructions Fenghua Yu
2020-06-13  0:41 ` [PATCH v2 06/12] x86/fpu/xstate: Add supervisor PASID state for ENQCMD feature Fenghua Yu
2020-06-13  0:41 ` [PATCH v2 07/12] x86/msr-index: Define IA32_PASID MSR Fenghua Yu
2020-06-13  0:41 ` [PATCH v2 08/12] mm: Define pasid in mm Fenghua Yu
2020-06-16  8:28   ` Jean-Philippe Brucker
2020-06-16 15:11     ` Fenghua Yu
2020-06-13  0:41 ` [PATCH v2 09/12] fork: Clear PASID for new mm Fenghua Yu
2020-06-13  0:41 ` [PATCH v2 10/12] x86/process: Clear PASID state for a newly forked/cloned thread Fenghua Yu
2020-06-13  0:41 ` [PATCH v2 11/12] x86/mmu: Allocate/free PASID Fenghua Yu
2020-06-13 13:07   ` Lu Baolu
2020-06-15  2:13   ` Lu Baolu
2020-06-13  0:41 ` [PATCH v2 12/12] x86/traps: Fix up invalid PASID Fenghua Yu
2020-06-15  7:53   ` Peter Zijlstra
2020-06-15  7:56   ` Peter Zijlstra
2020-06-15 15:48     ` Fenghua Yu
2020-06-15 16:03       ` Peter Zijlstra
2020-06-15 17:11         ` Luck, Tony
2020-06-15 18:12         ` Fenghua Yu
2020-06-15 18:31           ` Peter Zijlstra
2020-06-15 18:55             ` Fenghua Yu [this message]
2020-06-15 19:09               ` Peter Zijlstra
2020-06-15 20:17                 ` Fenghua Yu
2020-06-15 20:51                   ` Andy Lutomirski
2020-06-15 20:56                     ` Luck, Tony
2020-06-15 21:18                       ` Andy Lutomirski
2020-06-15 21:24                         ` Luck, Tony
2020-06-15 21:53                   ` Peter Zijlstra
2020-06-16 23:23                 ` Fenghua Yu
2020-06-17  8:31                   ` Peter Zijlstra
2020-06-15 18:19         ` Raj, Ashok
2020-06-15 18:32           ` Peter Zijlstra
2020-06-15  7:52 ` [PATCH v2 00/12] x86: tag application address space for devices Peter Zijlstra
2020-06-15 14:53   ` Fenghua Yu

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