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From: Andy Lutomirski <luto@kernel.org>
To: "Luck, Tony" <tony.luck@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@alien8.de>
Cc: "Yu, Fenghua" <fenghua.yu@intel.com>,
	linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	Ingo Molnar <mingo@redhat.com>, H Peter Anvin <hpa@zytor.com>,
	Jean-Philippe Brucker <jean-philippe@linaro.org>,
	Christoph Hellwig <hch@infradead.org>,
	Peter Zijlstra <peterz@infradead.org>,
	David Woodhouse <dwmw2@infradead.org>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	"Raj, Ashok" <ashok.raj@intel.com>,
	"Pan, Jacob jun" <jacob.jun.pan@intel.com>,
	"Jiang, Dave" <dave.jiang@intel.com>,
	"Mehta, Sohil" <sohil.mehta@intel.com>,
	"Shankar, Ravi V" <ravi.v.shankar@intel.com>
Subject: Re: [PATCH] x86/cpufeatures: Force disable X86_FEATURE_ENQCMD and remove update_pasid()
Date: Thu, 3 Jun 2021 10:31:36 -0700	[thread overview]
Message-ID: <db552f51-76ee-b7f5-20f1-14f1c703d423@kernel.org> (raw)
In-Reply-To: <36866b38ec92425b879881a88acf547b@intel.com>

On 6/2/21 1:37 PM, Luck, Tony wrote:
>>> ... so on a PASID system, your trivial reproducer would theoretically
>>> fire the same way and corrupt FPU state just as well.
>>
>> This is worse and you can't selftest it because the IPI can just hit in
>> the middle of _any_ FPU state operation and corrupt state.
> 
> That sounds like we should abandon the "IPI all the other threads
> to force enable the PASID for them" approach. It would just be a
> nightmare of papering over cracks when the IPI was delivered at
> some inconvenient moment when the recipient was in the middle
> of touching xsave state.
> 
> I've told Fenghua to dig out the previous iteration of this patch where
> the plan was to lazily fix the PASID_MSR in other threads in the #GP
> handler.

Blech.  Also this won't work for other PASID-like features.

I have a half-written patch to fix this up for real.  Stay tuned.

> Seems like a better direction than trying to fix the IPI method. The virtualization
> folks will like this way more because IPI in guest causes a couple of VMEXIT
> so is somewhat expensive.

It happens at most once per PASID-using process.


WARNING: multiple messages have this Message-ID (diff)
From: Andy Lutomirski <luto@kernel.org>
To: "Luck, Tony" <tony.luck@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	 Borislav Petkov <bp@alien8.de>
Cc: "Yu, Fenghua" <fenghua.yu@intel.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	"Jiang, Dave" <dave.jiang@intel.com>,
	"Raj, Ashok" <ashok.raj@intel.com>,
	"Shankar, Ravi V" <ravi.v.shankar@intel.com>,
	Jean-Philippe Brucker <jean-philippe@linaro.org>,
	Peter Zijlstra <peterz@infradead.org>, x86 <x86@kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Christoph Hellwig <hch@infradead.org>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	Ingo Molnar <mingo@redhat.com>,
	"Pan, Jacob jun" <jacob.jun.pan@intel.com>,
	H Peter Anvin <hpa@zytor.com>,
	David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH] x86/cpufeatures: Force disable X86_FEATURE_ENQCMD and remove update_pasid()
Date: Thu, 3 Jun 2021 10:31:36 -0700	[thread overview]
Message-ID: <db552f51-76ee-b7f5-20f1-14f1c703d423@kernel.org> (raw)
In-Reply-To: <36866b38ec92425b879881a88acf547b@intel.com>

On 6/2/21 1:37 PM, Luck, Tony wrote:
>>> ... so on a PASID system, your trivial reproducer would theoretically
>>> fire the same way and corrupt FPU state just as well.
>>
>> This is worse and you can't selftest it because the IPI can just hit in
>> the middle of _any_ FPU state operation and corrupt state.
> 
> That sounds like we should abandon the "IPI all the other threads
> to force enable the PASID for them" approach. It would just be a
> nightmare of papering over cracks when the IPI was delivered at
> some inconvenient moment when the recipient was in the middle
> of touching xsave state.
> 
> I've told Fenghua to dig out the previous iteration of this patch where
> the plan was to lazily fix the PASID_MSR in other threads in the #GP
> handler.

Blech.  Also this won't work for other PASID-like features.

I have a half-written patch to fix this up for real.  Stay tuned.

> Seems like a better direction than trying to fix the IPI method. The virtualization
> folks will like this way more because IPI in guest causes a couple of VMEXIT
> so is somewhat expensive.

It happens at most once per PASID-using process.

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  reply	other threads:[~2021-06-03 17:31 UTC|newest]

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-15 16:30 [PATCH v8 0/9] x86: tag application address space for devices Fenghua Yu
2020-09-15 16:30 ` [PATCH v8 1/9] drm, iommu: Change type of pasid to u32 Fenghua Yu
2020-09-18  7:42   ` [tip: x86/pasid] " tip-bot2 for Fenghua Yu
2020-09-15 16:30 ` [PATCH v8 2/9] iommu/vt-d: Change flags type to unsigned int in binding mm Fenghua Yu
2020-09-15 16:30   ` Fenghua Yu
2020-09-18  7:42   ` [tip: x86/pasid] " tip-bot2 for Fenghua Yu
2020-09-15 16:30 ` [PATCH v8 3/9] Documentation/x86: Add documentation for SVA (Shared Virtual Addressing) Fenghua Yu
2020-09-17  7:53   ` Borislav Petkov
2020-09-17  7:53     ` Borislav Petkov
2020-09-17 14:56     ` Raj, Ashok
2020-09-17 14:56       ` Raj, Ashok
2020-09-17 17:18       ` Borislav Petkov
2020-09-17 17:18         ` Borislav Petkov
2020-09-17 17:22         ` Raj, Ashok
2020-09-17 17:22           ` Raj, Ashok
2020-09-17 17:30           ` Borislav Petkov
2020-09-17 17:30             ` Borislav Petkov
2020-09-18 16:22             ` Fenghua Yu
2020-09-18 16:22               ` Fenghua Yu
2020-09-18  7:42   ` [tip: x86/pasid] " tip-bot2 for Ashok Raj
2020-09-15 16:30 ` [PATCH v8 4/9] x86/cpufeatures: Enumerate ENQCMD and ENQCMDS instructions Fenghua Yu
2020-09-15 16:30   ` Fenghua Yu
2020-09-18  7:42   ` [tip: x86/pasid] " tip-bot2 for Fenghua Yu
2020-09-15 16:30 ` [PATCH v8 5/9] x86/fpu/xstate: Add supervisor PASID state for ENQCMD feature Fenghua Yu
2020-09-15 16:30   ` Fenghua Yu
2020-09-18  7:42   ` [tip: x86/pasid] x86/fpu/xstate: Add supervisor PASID state for ENQCMD tip-bot2 for Yu-cheng Yu
2020-09-15 16:30 ` [PATCH v8 6/9] x86/msr-index: Define IA32_PASID MSR Fenghua Yu
2020-09-15 16:30   ` Fenghua Yu
2020-09-18  7:42   ` [tip: x86/pasid] x86/msr-index: Define an " tip-bot2 for Fenghua Yu
2020-09-15 16:30 ` [PATCH v8 7/9] mm: Define pasid in mm Fenghua Yu
2020-09-18  7:42   ` [tip: x86/pasid] mm: Add a pasid member to struct mm_struct tip-bot2 for Fenghua Yu
2020-09-15 16:30 ` [PATCH v8 8/9] x86/cpufeatures: Mark ENQCMD as disabled when configured out Fenghua Yu
2020-09-18  7:42   ` [tip: x86/pasid] " tip-bot2 for Fenghua Yu
2020-09-15 16:30 ` [PATCH v8 9/9] x86/mmu: Allocate/free PASID Fenghua Yu
2020-09-15 16:30   ` Fenghua Yu
2020-09-18  7:42   ` [tip: x86/pasid] x86/mmu: Allocate/free a PASID tip-bot2 for Fenghua Yu
2021-05-29  9:17   ` [PATCH] x86/cpufeatures: Force disable X86_FEATURE_ENQCMD and remove update_pasid() Thomas Gleixner
2021-05-29  9:17     ` Thomas Gleixner
2021-05-31  8:43     ` Borislav Petkov
2021-05-31  8:43       ` Borislav Petkov
2021-05-31 10:16       ` Thomas Gleixner
2021-05-31 10:16         ` Thomas Gleixner
2021-06-02 20:37         ` Luck, Tony
2021-06-02 20:37           ` Luck, Tony
2021-06-03 17:31           ` Andy Lutomirski [this message]
2021-06-03 17:31             ` Andy Lutomirski
2021-06-09 17:32             ` Luck, Tony
2021-06-09 17:32               ` Luck, Tony
2021-06-09 23:34               ` Andy Lutomirski
2021-06-09 23:34                 ` Andy Lutomirski
2021-06-25 15:46                 ` Luck, Tony
2021-06-25 15:46                   ` Luck, Tony
2021-06-02 10:14     ` Borislav Petkov
2021-06-02 10:14       ` Borislav Petkov
2021-06-02 10:20       ` Thomas Gleixner
2021-06-02 10:20         ` Thomas Gleixner
2021-06-03 11:20       ` Vinod Koul
2021-06-03 11:20         ` Vinod Koul
2021-06-03 11:42         ` Borislav Petkov
2021-06-03 11:42           ` Borislav Petkov
2021-06-03 12:47           ` Vinod Koul
2021-06-03 12:47             ` Vinod Koul
2021-06-03 14:33             ` Borislav Petkov
2021-06-03 14:33               ` Borislav Petkov
2021-06-02 19:49     ` [tip: x86/urgent] " tip-bot2 for Thomas Gleixner
2021-06-03 14:38     ` tip-bot2 for Thomas Gleixner
2020-09-16  8:06 ` [PATCH v8 0/9] x86: tag application address space for devices Joerg Roedel
2020-09-16  8:06   ` Joerg Roedel
2020-09-17 23:53   ` Fenghua Yu
2020-09-17 23:53     ` Fenghua Yu

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