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([2600:100e:b12a:ccdd:512d:55a6:36a5:bcd4]) by smtp.gmail.com with ESMTPSA id g73sm41439912pfd.185.2019.04.05.09.27.08 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 05 Apr 2019 09:27:08 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (1.0) Subject: Re: [RFC PATCH v9 12/13] xpfo, mm: Defer TLB flushes for non-current CPUs (x86 only) From: Andy Lutomirski X-Mailer: iPhone Mail (16D57) In-Reply-To: <36b999d4-adf6-08a3-2897-d77b9cba20f8@intel.com> Date: Fri, 5 Apr 2019 10:27:05 -0600 Cc: Thomas Gleixner , Khalid Aziz , Andy Lutomirski , Juerg Haefliger , Tycho Andersen , jsteckli@amazon.de, Andi Kleen , liran.alon@oracle.com, Kees Cook , Konrad Rzeszutek Wilk , deepa.srinivasan@oracle.com, chris hyser , Tyler Hicks , "Woodhouse, David" , Andrew Cooper , Jon Masters , Boris Ostrovsky , kanth.ghatraju@oracle.com, Joao Martins , Jim Mattson , pradeep.vincent@oracle.com, John Haxby , "Kirill A. Shutemov" , Christoph Hellwig , steven.sistare@oracle.com, Laura Abbott , Peter Zijlstra , Aaron Lu , Andrew Morton , alexander.h.duyck@linux.intel.com, Amir Goldstein , Andrey Konovalov , aneesh.kumar@linux.ibm.com, anthony.yznaga@oracle.com, Ard Biesheuvel , Arnd Bergmann , arunks@codeaurora.org, Ben Hutchings , Sebastian Andrzej Siewior , Borislav Petkov , brgl@bgdev.pl, Catalin Marinas , Jonathan Corbet , cpandya@codeaurora.org, Daniel Vetter , Dan Williams , Greg KH , Roman Gushchin , Johannes Weiner , "H. Peter Anvin" , Joonsoo Kim , James Morse , Jann Horn , Juergen Gross , Jiri Kosina , James Morris , Joe Perches , Souptick Joarder , Joerg Roedel , Keith Busch , Konstantin Khlebnikov , Logan Gunthorpe , marco.antonio.780@gmail.com, Mark Rutland , Mel Gorman , Michal Hocko , Michal Hocko , Mike Kravetz , Ingo Molnar , "Michael S. Tsirkin" , Marek Szyprowski , Nicholas Piggin , osalvador@suse.de, "Paul E. McKenney" , pavel.tatashin@microsoft.com, Randy Dunlap , richard.weiyang@gmail.com, Rik van Riel , David Rientjes , Robin Murphy , Steven Rostedt , Mike Rapoport , Sai Praneeth Prakhya , "Serge E. Hallyn" , Steve Capper , thymovanbeers@gmail.com, Vlastimil Babka , Will Deacon , Matthew Wilcox , yaojun8558363@gmail.com, Huang Ying , zhangshaokun@hisilicon.com, iommu@lists.linux-foundation.org, X86 ML , linux-arm-kernel , LKML , Linux-MM , LSM List , Khalid Aziz Content-Transfer-Encoding: quoted-printable Message-Id: References: <4495dda4bfc4a06b3312cc4063915b306ecfaecb.1554248002.git.khalid.aziz@oracle.com> <91f1dbce-332e-25d1-15f6-0e9cfc8b797b@oracle.com> <26b00051-b03c-9fce-1446-52f0d6ed52f8@intel.com> <36b999d4-adf6-08a3-2897-d77b9cba20f8@intel.com> To: Dave Hansen X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > On Apr 5, 2019, at 10:01 AM, Dave Hansen wrote: >=20 > On 4/5/19 8:24 AM, Andy Lutomirski wrote: >>> Sounds like we need a mechanism that will do the deferred XPFO TLB=20 >>> flushes whenever the kernel is entered, and not _just_ at context >>> switch time. This permits an app to run in userspace with stale >>> kernel TLB entries as long as it wants... that's harmless. > ... >> I suppose we could do the flush at context switch *and* >> entry. I bet that performance still utterly sucks, though =E2=80=94 on m= any >> workloads, this turns every entry into a full flush, and we already >> know exactly how much that sucks =E2=80=94 it=E2=80=99s identical to KPTI= without >> PCID. (And yes, if we go this route, we need to merge this logic >> together =E2=80=94 we shouldn=E2=80=99t write CR3 twice on entry). >=20 > Yeah, probably true. >=20 > Just eyeballing this, it would mean mapping the "cpu needs deferred > flush" variable into the cpu_entry_area, which doesn't seem too awful. >=20 > I think the basic overall concern is that the deferred flush leaves too > many holes and by the time we close them sufficiently, performance will > suck again. Seems like a totally valid concern, but my crystal ball is > hazy on whether it will be worth it in the end to many folks >=20 > ... >> In other words, I think that ret2dir is an insufficient justification >> for XPFO. >=20 > Yeah, other things that it is good for have kinda been lost in the > noise. I think I first started looking at this long before Meltdown and > L1TF were public. >=20 > There are hypervisors out there that simply don't (persistently) map > user data. They can't leak user data because they don't even have > access to it in their virtual address space. Those hypervisors had a > much easier time with L1TF mitigation than we did. Basically, they > could flush the L1 after user data was accessible instead of before > untrusted guest code runs. >=20 > My hope is that XPFO could provide us similar protection. But, > somebody's got to poke at it for a while to see how far they can push it. >=20 > IMNHO, XPFO is *always* going to be painful for kernel compiles. But, > cloud providers aren't doing a lot of kernel compiles on their KVM > hosts, and they deeply care about leaking their users' data. At the risk of asking stupid questions: we already have a mechanism for this= : highmem. Can we enable highmem on x86_64, maybe with some heuristics to m= ake it work well?= From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Lutomirski Subject: Re: [RFC PATCH v9 12/13] xpfo, mm: Defer TLB flushes for non-current CPUs (x86 only) Date: Fri, 5 Apr 2019 10:27:05 -0600 Message-ID: References: <4495dda4bfc4a06b3312cc4063915b306ecfaecb.1554248002.git.khalid.aziz@oracle.com> <91f1dbce-332e-25d1-15f6-0e9cfc8b797b@oracle.com> <26b00051-b03c-9fce-1446-52f0d6ed52f8@intel.com> <36b999d4-adf6-08a3-2897-d77b9cba20f8@intel.com> Mime-Version: 1.0 (1.0) Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: In-Reply-To: <36b999d4-adf6-08a3-2897-d77b9cba20f8-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Dave Hansen Cc: Catalin Marinas , Will Deacon , Khalid Aziz , steven.sistare-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org, Christoph Hellwig , Tycho Andersen , Andi Kleen , aneesh.kumar-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org, James Morris , David Rientjes , anthony.yznaga-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org, Rik van Riel , Nicholas Piggin , Mike Rapoport , Andy Lutomirski , Thomas Gleixner , Greg KH , Randy Dunlap , LKML , Souptick Joarder , Jiri Kosina , Joe Perches , arunks-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org, Andrew Morton , "Woodhouse, David" , Mark List-Id: iommu@lists.linux-foundation.org Cgo+IE9uIEFwciA1LCAyMDE5LCBhdCAxMDowMSBBTSwgRGF2ZSBIYW5zZW4gPGRhdmUuaGFuc2Vu QGludGVsLmNvbT4gd3JvdGU6Cj4gCj4gT24gNC81LzE5IDg6MjQgQU0sIEFuZHkgTHV0b21pcnNr aSB3cm90ZToKPj4+IFNvdW5kcyBsaWtlIHdlIG5lZWQgYSBtZWNoYW5pc20gdGhhdCB3aWxsIGRv IHRoZSBkZWZlcnJlZCBYUEZPIFRMQiAKPj4+IGZsdXNoZXMgd2hlbmV2ZXIgdGhlIGtlcm5lbCBp cyBlbnRlcmVkLCBhbmQgbm90IF9qdXN0XyBhdCBjb250ZXh0Cj4+PiBzd2l0Y2ggdGltZS4gIFRo 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([2600:100e:b12a:ccdd:512d:55a6:36a5:bcd4]) by smtp.gmail.com with ESMTPSA id g73sm41439912pfd.185.2019.04.05.09.27.08 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 05 Apr 2019 09:27:08 -0700 (PDT) Mime-Version: 1.0 (1.0) Subject: Re: [RFC PATCH v9 12/13] xpfo, mm: Defer TLB flushes for non-current CPUs (x86 only) From: Andy Lutomirski X-Mailer: iPhone Mail (16D57) In-Reply-To: <36b999d4-adf6-08a3-2897-d77b9cba20f8@intel.com> Date: Fri, 5 Apr 2019 10:27:05 -0600 Message-Id: References: <4495dda4bfc4a06b3312cc4063915b306ecfaecb.1554248002.git.khalid.aziz@oracle.com> <91f1dbce-332e-25d1-15f6-0e9cfc8b797b@oracle.com> <26b00051-b03c-9fce-1446-52f0d6ed52f8@intel.com> <36b999d4-adf6-08a3-2897-d77b9cba20f8@intel.com> To: Dave Hansen Cc: Catalin Marinas , Will Deacon , Khalid Aziz , steven.sistare@oracle.com, Christoph Hellwig , Tycho Andersen , Andi Kleen , aneesh.kumar@linux.ibm.com, James Morris , David Rientjes , anthony.yznaga@oracle.com, Rik van Riel , Nicholas Piggin , Mike Rapoport , Andy Lutomirski , Thomas Gleixner , Greg KH , Randy Dunlap , LKML , Souptick Joarder , Jiri Kosina , Joe Perches , arunks@codeaurora.org, Andrew Morton , "Woodhouse, David" , Mark Rutland , Keith Busch , Joao Martins , "H. 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Tsirkin" , Peter Zijlstra , Daniel Vetter , Sebastian Andrzej Siewior , Amir Goldstein , Linux-MM , deepa.srinivasan@oracle.com, cpandya@codeaurora.org, X86 ML , yaojun8558363@gmail.com, Ingo Molnar , Jon Masters , thymovanbeers@gmail.com, Laura Abbott , pradeep.vincent@oracle.com, pavel.tatashin@microsoft.com, Jann Horn , Vlastimil Babka , Jim Mattson , Juergen Gross , marco.antonio.780@gmail.com, Juerg Haefliger , Mel Gorman , Tyler Hicks , John Haxby , LSM List , Johannes Weiner , liran.alon@oracle.com, Robin Murphy X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: base64 Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org Message-ID: <20190405162705.80qKVwelRsIzWCNO9w-OFGnbqakBr-0bEs04OgKc46w@z> Cgo+IE9uIEFwciA1LCAyMDE5LCBhdCAxMDowMSBBTSwgRGF2ZSBIYW5zZW4gPGRhdmUuaGFuc2Vu QGludGVsLmNvbT4gd3JvdGU6Cj4gCj4gT24gNC81LzE5IDg6MjQgQU0sIEFuZHkgTHV0b21pcnNr aSB3cm90ZToKPj4+IFNvdW5kcyBsaWtlIHdlIG5lZWQgYSBtZWNoYW5pc20gdGhhdCB3aWxsIGRv IHRoZSBkZWZlcnJlZCBYUEZPIFRMQiAKPj4+IGZsdXNoZXMgd2hlbmV2ZXIgdGhlIGtlcm5lbCBp cyBlbnRlcmVkLCBhbmQgbm90IF9qdXN0XyBhdCBjb250ZXh0Cj4+PiBzd2l0Y2ggdGltZS4gIFRo aXMgcGVybWl0cyBhbiBhcHAgdG8gcnVuIGluIHVzZXJzcGFjZSB3aXRoIHN0YWxlCj4+PiBrZXJu ZWwgVExCIGVudHJpZXMgYXMgbG9uZyBhcyBpdCB3YW50cy4uLiB0aGF0J3MgaGFybWxlc3MuCj4g Li4uCj4+IEkgc3VwcG9zZSB3ZSBjb3VsZCBkbyB0aGUgZmx1c2ggYXQgY29udGV4dCBzd2l0Y2gg KmFuZCoKPj4gZW50cnkuICBJIGJldCB0aGF0IHBlcmZvcm1hbmNlIHN0aWxsIHV0dGVybHkgc3Vj a3MsIHRob3VnaCDigJQgb24gbWFueQo+PiB3b3JrbG9hZHMsIHRoaXMgdHVybnMgZXZlcnkgZW50 cnkgaW50byBhIGZ1bGwgZmx1c2gsIGFuZCB3ZSBhbHJlYWR5Cj4+IGtub3cgZXhhY3RseSBob3cg bXVjaCB0aGF0IHN1Y2tzIOKAlCBpdOKAmXMgaWRlbnRpY2FsIHRvIEtQVEkgd2l0aG91dAo+PiBQ Q0lELiAgKEFuZCB5ZXMsIGlmIHdlIGdvIHRoaXMgcm91dGUsIHdlIG5lZWQgdG8gbWVyZ2UgdGhp cyBsb2dpYwo+PiB0b2dldGhlciDigJQgd2Ugc2hvdWxkbuKAmXQgd3JpdGUgQ1IzIHR3aWNlIG9u IGVudHJ5KS4KPiAKPiBZZWFoLCBwcm9iYWJseSB0cnVlLgo+IAo+IEp1c3QgZXllYmFsbGluZyB0 aGlzLCBpdCB3b3VsZCBtZWFuIG1hcHBpbmcgdGhlICJjcHUgbmVlZHMgZGVmZXJyZWQKPiBmbHVz aCIgdmFyaWFibGUgaW50byB0aGUgY3B1X2VudHJ5X2FyZWEsIHdoaWNoIGRvZXNuJ3Qgc2VlbSB0 b28gYXdmdWwuCj4gCj4gSSB0aGluayB0aGUgYmFzaWMgb3ZlcmFsbCBjb25jZXJuIGlzIHRoYXQg dGhlIGRlZmVycmVkIGZsdXNoIGxlYXZlcyB0b28KPiBtYW55IGhvbGVzIGFuZCBieSB0aGUgdGlt ZSB3ZSBjbG9zZSB0aGVtIHN1ZmZpY2llbnRseSwgcGVyZm9ybWFuY2Ugd2lsbAo+IHN1Y2sgYWdh aW4uICBTZWVtcyBsaWtlIGEgdG90YWxseSB2YWxpZCBjb25jZXJuLCBidXQgbXkgY3J5c3RhbCBi YWxsIGlzCj4gaGF6eSBvbiB3aGV0aGVyIGl0IHdpbGwgYmUgd29ydGggaXQgaW4gdGhlIGVuZCB0 byBtYW55IGZvbGtzCj4gCj4gLi4uCj4+IEluIG90aGVyIHdvcmRzLCBJIHRoaW5rIHRoYXQgcmV0 MmRpciBpcyBhbiBpbnN1ZmZpY2llbnQganVzdGlmaWNhdGlvbgo+PiBmb3IgWFBGTy4KPiAKPiBZ ZWFoLCBvdGhlciB0aGluZ3MgdGhhdCBpdCBpcyBnb29kIGZvciBoYXZlIGtpbmRhIGJlZW4gbG9z dCBpbiB0aGUKPiBub2lzZS4gIEkgdGhpbmsgSSBmaXJzdCBzdGFydGVkIGxvb2tpbmcgYXQgdGhp cyBsb25nIGJlZm9yZSBNZWx0ZG93biBhbmQKPiBMMVRGIHdlcmUgcHVibGljLgo+IAo+IFRoZXJl IGFyZSBoeXBlcnZpc29ycyBvdXQgdGhlcmUgdGhhdCBzaW1wbHkgZG9uJ3QgKHBlcnNpc3RlbnRs eSkgbWFwCj4gdXNlciBkYXRhLiAgVGhleSBjYW4ndCBsZWFrIHVzZXIgZGF0YSBiZWNhdXNlIHRo ZXkgZG9uJ3QgZXZlbiBoYXZlCj4gYWNjZXNzIHRvIGl0IGluIHRoZWlyIHZpcnR1YWwgYWRkcmVz cyBzcGFjZS4gIFRob3NlIGh5cGVydmlzb3JzIGhhZCBhCj4gbXVjaCBlYXNpZXIgdGltZSB3aXRo IEwxVEYgbWl0aWdhdGlvbiB0aGFuIHdlIGRpZC4gIEJhc2ljYWxseSwgdGhleQo+IGNvdWxkIGZs dXNoIHRoZSBMMSBhZnRlciB1c2VyIGRhdGEgd2FzIGFjY2Vzc2libGUgaW5zdGVhZCBvZiBiZWZv cmUKPiB1bnRydXN0ZWQgZ3Vlc3QgY29kZSBydW5zLgo+IAo+IE15IGhvcGUgaXMgdGhhdCBYUEZP IGNvdWxkIHByb3ZpZGUgdXMgc2ltaWxhciBwcm90ZWN0aW9uLiAgQnV0LAo+IHNvbWVib2R5J3Mg Z290IHRvIHBva2UgYXQgaXQgZm9yIGEgd2hpbGUgdG8gc2VlIGhvdyBmYXIgdGhleSBjYW4gcHVz aCBpdC4KPiAKPiBJTU5ITywgWFBGTyBpcyAqYWx3YXlzKiBnb2luZyB0byBiZSBwYWluZnVsIGZv ciBrZXJuZWwgY29tcGlsZXMuICBCdXQsCj4gY2xvdWQgcHJvdmlkZXJzIGFyZW4ndCBkb2luZyBh IGxvdCBvZiBrZXJuZWwgY29tcGlsZXMgb24gdGhlaXIgS1ZNCj4gaG9zdHMsIGFuZCB0aGV5IGRl ZXBseSBjYXJlIGFib3V0IGxlYWtpbmcgdGhlaXIgdXNlcnMnIGRhdGEuCgpBdCB0aGUgcmlzayBv ZiBhc2tpbmcgc3R1cGlkIHF1ZXN0aW9uczogd2UgYWxyZWFkeSBoYXZlIGEgbWVjaGFuaXNtIGZv ciB0aGlzOiBoaWdobWVtLiAgQ2FuIHdlIGVuYWJsZSBoaWdobWVtIG9uIHg4Nl82NCwgbWF5YmUg d2l0aCBzb21lIGhldXJpc3RpY3MgdG8gbWFrZSBpdCB3b3JrIHdlbGw/Cl9fX19fX19fX19fX19f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fCmlvbW11IG1haWxpbmcgbGlzdAppb21t dUBsaXN0cy5saW51eC1mb3VuZGF0aW9uLm9yZwpodHRwczovL2xpc3RzLmxpbnV4Zm91bmRhdGlv bi5vcmcvbWFpbG1hbi9saXN0aW5mby9pb21tdQ==