From: David Hildenbrand <david@redhat.com> To: Christian Borntraeger <borntraeger@de.ibm.com>, Janosch Frank <frankja@linux.vnet.ibm.com>, Andrew Morton <akpm@linux-foundation.org> Cc: KVM <kvm@vger.kernel.org>, Cornelia Huck <cohuck@redhat.com>, Thomas Huth <thuth@redhat.com>, Ulrich Weigand <Ulrich.Weigand@de.ibm.com>, Claudio Imbrenda <imbrenda@linux.ibm.com>, linux-s390 <linux-s390@vger.kernel.org>, Michael Mueller <mimu@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>, Andrea Arcangeli <aarcange@redhat.com>, linux-mm@kvack.org, Will Deacon <will@kernel.org>, Sean Christopherson <sean.j.christopherson@intel.com> Subject: Re: [PATCH v2 01/42] mm:gup/writeback: add callbacks for inaccessible pages Date: Tue, 18 Feb 2020 09:27:20 +0100 Message-ID: <a8f8786e-1ed0-0c44-08d0-ebc58f43ae40@redhat.com> (raw) In-Reply-To: <dd33cc1a-214d-b949-8f5e-9c2d40a8e518@de.ibm.com> On 17.02.20 12:10, Christian Borntraeger wrote: > > > On 17.02.20 10:14, David Hildenbrand wrote: >> On 14.02.20 23:26, Christian Borntraeger wrote: >>> From: Claudio Imbrenda <imbrenda@linux.ibm.com> >>> >>> With the introduction of protected KVM guests on s390 there is now a >>> concept of inaccessible pages. These pages need to be made accessible >>> before the host can access them. >>> >>> While cpu accesses will trigger a fault that can be resolved, I/O >>> accesses will just fail. We need to add a callback into architecture >>> code for places that will do I/O, namely when writeback is started or >>> when a page reference is taken. >>> >>> This is not only to enable paging, file backing etc, it is also >>> necessary to protect the host against a malicious user space. For >>> example a bad QEMU could simply start direct I/O on such protected >>> memory. We do not want userspace to be able to trigger I/O errors and >>> thus we the logic is "whenever somebody accesses that page (gup) or >>> doing I/O, make sure that this page can be accessed. When the guest >>> tries to access that page we will wait in the page fault handler for >>> writeback to have finished and for the page_ref to be the expected >>> value. >>> >>> If wanted by others, the callbacks can be extended with error handlin >>> and a parameter from where this is called. >> >> s/handlin/handling/ > > ack. >> >> One last question from my side: >> >> Why is it OK to ignore errors here. IOW, why not squash "[PATCH v2 >> 39/42] example for future extension: mm:gup/writeback: add callbacks for >> inaccessible pages: error cases" into this patch. > > I can certainly squash this in. But I have never heard feedback from the > memory management people if they would prefer the patch as-is (no overhead > at all for !s390) or already with the error handling. >> >> I can see in patch "[PATCH v2 05/42] s390/mm: provide memory management >> functions for protected KVM guests", that the call can fail for various >> reasons. That puzzles me a bit - what would happen if any of that fails? > > The convert _to_ secure has error handling. uv_convert_from_secure (the > one that is used for arch_make_page_accessible can only fail if we mess up, > e.g. an "export" on memory that we have donated to the ultravisor. Okay, so more like a BUG_ON() in case it really fails. > > >> Or will it actually never fail for s390x (and all that error handling in >> arch_make_page_accessible() is essentially dead code in real life?) > > So yes, if everything is setup properly this should not fail in real life > and only we have a kernel (or firmware) bug. > Then, without feedback from other possible users, this should be a void function. So either introduce error handling or convert it to a void for now (and add e.g., BUG_ON and a comment inside the s390x implementation). As discussed in the other patch, I'd prefer a CONFIG_HAVE_ARCH_MAKE_PAGE_ACCESSIBLE and handle it via kconfig, but not sure what other people here prefer. -- Thanks, David / dhildenb
next prev parent reply index Thread overview: 132+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-02-14 22:26 [PATCH v2 00/42] KVM: s390: Add support for protected VMs Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 01/42] mm:gup/writeback: add callbacks for inaccessible pages Christian Borntraeger 2020-02-17 9:14 ` David Hildenbrand 2020-02-17 11:10 ` Christian Borntraeger 2020-02-18 8:27 ` David Hildenbrand [this message] 2020-02-18 15:46 ` Sean Christopherson 2020-02-18 16:02 ` Will Deacon 2020-02-18 16:15 ` Christian Borntraeger 2020-02-18 21:35 ` Sean Christopherson 2020-02-19 8:31 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 02/42] KVM: s390/interrupt: do not pin adapter interrupt pages Christian Borntraeger 2020-02-17 9:43 ` David Hildenbrand 2020-02-20 12:18 ` David Hildenbrand 2020-02-20 13:31 ` Christian Borntraeger 2020-02-20 13:34 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 03/42] s390/protvirt: introduce host side setup Christian Borntraeger 2020-02-17 9:53 ` David Hildenbrand 2020-02-17 11:11 ` Christian Borntraeger 2020-02-17 11:13 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 04/42] s390/protvirt: add ultravisor initialization Christian Borntraeger 2020-02-17 9:57 ` David Hildenbrand 2020-02-17 11:13 ` Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 05/42] s390/mm: provide memory management functions for protected KVM guests Christian Borntraeger 2020-02-17 10:21 ` David Hildenbrand 2020-02-17 11:28 ` Christian Borntraeger 2020-02-17 12:07 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 06/42] s390/mm: add (non)secure page access exceptions handlers Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 07/42] KVM: s390: protvirt: Add UV debug trace Christian Borntraeger 2020-02-17 10:41 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 08/42] KVM: s390: add new variants of UV CALL Christian Borntraeger 2020-02-17 10:42 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 09/42] KVM: s390: protvirt: Add initial vm and cpu lifecycle handling Christian Borntraeger 2020-02-17 10:56 ` David Hildenbrand 2020-02-17 12:04 ` Christian Borntraeger 2020-02-17 12:09 ` David Hildenbrand 2020-02-17 14:53 ` [PATCH 0/2] example changes Christian Borntraeger 2020-02-17 14:53 ` [PATCH 1/2] lock changes Christian Borntraeger 2020-02-17 14:53 ` [PATCH 2/2] merge vm/cpu create Christian Borntraeger 2020-02-17 15:00 ` Janosch Frank 2020-02-17 15:02 ` Christian Borntraeger 2020-02-19 11:02 ` Christian Borntraeger 2020-02-17 19:18 ` [PATCH 0/2] example changes David Hildenbrand 2020-02-18 8:09 ` [PATCH v2 09/42] KVM: s390: protvirt: Add initial vm and cpu lifecycle handling Christian Borntraeger 2020-02-18 8:39 ` [PATCH v2.1] " Christian Borntraeger 2020-02-18 9:12 ` David Hildenbrand 2020-02-18 21:18 ` Christian Borntraeger 2020-02-19 8:32 ` David Hildenbrand 2020-02-19 11:01 ` Christian Borntraeger 2020-02-18 9:56 ` David Hildenbrand 2020-02-18 20:26 ` Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 10/42] KVM: s390: protvirt: Add KVM api documentation Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 11/42] KVM: s390: protvirt: Secure memory is not mergeable Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 12/42] KVM: s390/mm: Make pages accessible before destroying the guest Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 13/42] KVM: s390: protvirt: Handle SE notification interceptions Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 14/42] KVM: s390: protvirt: Instruction emulation Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 15/42] KVM: s390: protvirt: Add interruption injection controls Christian Borntraeger 2020-02-17 10:59 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 16/42] KVM: s390: protvirt: Implement interruption injection Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 17/42] KVM: s390: protvirt: Add SCLP interrupt handling Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 18/42] KVM: s390: protvirt: Handle spec exception loops Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 19/42] KVM: s390: protvirt: Add new gprs location handling Christian Borntraeger 2020-02-17 11:01 ` David Hildenbrand 2020-02-17 11:33 ` Christian Borntraeger 2020-02-17 14:37 ` Janosch Frank 2020-02-14 22:26 ` [PATCH v2 20/42] KVM: S390: protvirt: Introduce instruction data area bounce buffer Christian Borntraeger 2020-02-17 11:08 ` David Hildenbrand 2020-02-17 14:47 ` Janosch Frank 2020-02-17 15:00 ` Christian Borntraeger 2020-02-17 15:38 ` Janosch Frank 2020-02-17 16:58 ` Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 21/42] KVM: s390: protvirt: handle secure guest prefix pages Christian Borntraeger 2020-02-17 11:11 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 22/42] KVM: s390/mm: handle guest unpin events Christian Borntraeger 2020-02-17 14:23 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 23/42] KVM: s390: protvirt: Write sthyi data to instruction data area Christian Borntraeger 2020-02-17 14:24 ` David Hildenbrand 2020-02-17 18:40 ` Christian Borntraeger 2020-02-17 19:16 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 24/42] KVM: s390: protvirt: STSI handling Christian Borntraeger 2020-02-18 8:35 ` David Hildenbrand 2020-02-18 8:44 ` Christian Borntraeger 2020-02-18 9:08 ` David Hildenbrand 2020-02-18 9:11 ` Christian Borntraeger 2020-02-18 9:13 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 25/42] KVM: s390: protvirt: disallow one_reg Christian Borntraeger 2020-02-18 8:40 ` David Hildenbrand 2020-02-18 8:57 ` Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 26/42] KVM: s390: protvirt: Do only reset registers that are accessible Christian Borntraeger 2020-02-18 8:42 ` David Hildenbrand 2020-02-18 9:20 ` Christian Borntraeger 2020-02-18 9:28 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 27/42] KVM: s390: protvirt: Only sync fmt4 registers Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 28/42] KVM: s390: protvirt: Add program exception injection Christian Borntraeger 2020-02-18 9:33 ` David Hildenbrand 2020-02-18 9:37 ` Christian Borntraeger 2020-02-18 9:39 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 29/42] KVM: s390: protvirt: Add diag 308 subcode 8 - 10 handling Christian Borntraeger 2020-02-18 9:38 ` David Hildenbrand 2020-02-19 12:45 ` Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 30/42] KVM: s390: protvirt: UV calls in support of diag308 0, 1 Christian Borntraeger 2020-02-18 9:44 ` David Hildenbrand 2020-02-19 11:53 ` Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 31/42] KVM: s390: protvirt: Report CPU state to Ultravisor Christian Borntraeger 2020-02-18 9:48 ` David Hildenbrand 2020-02-19 19:36 ` Christian Borntraeger 2020-02-19 19:46 ` Christian Borntraeger 2020-02-20 10:52 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 32/42] KVM: s390: protvirt: Support cmd 5 operation state Christian Borntraeger 2020-02-18 9:50 ` David Hildenbrand 2020-02-19 11:06 ` Christian Borntraeger 2020-02-19 11:08 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 33/42] KVM: s390: protvirt: Mask PSW interrupt bits for interception 104 and 112 Christian Borntraeger 2020-02-18 9:53 ` David Hildenbrand 2020-02-18 10:02 ` David Hildenbrand 2020-02-18 10:05 ` Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 34/42] KVM: s390: protvirt: do not inject interrupts after start Christian Borntraeger 2020-02-18 9:53 ` David Hildenbrand 2020-02-18 10:02 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 35/42] KVM: s390: protvirt: Add UV cpu reset calls Christian Borntraeger 2020-02-18 9:54 ` David Hildenbrand 2020-02-14 22:26 ` [PATCH v2 36/42] DOCUMENTATION: Protected virtual machine introduction and IPL Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 37/42] s390/uv: Fix handling of length extensions (already in s390 tree) Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 38/42] s390: protvirt: Add sysfs firmware interface for Ultravisor information Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 39/42] example for future extension: mm:gup/writeback: add callbacks for inaccessible pages: error cases Christian Borntraeger 2020-02-18 16:25 ` Will Deacon 2020-02-18 16:30 ` Christian Borntraeger 2020-02-18 16:33 ` Will Deacon 2020-02-14 22:26 ` [PATCH v2 40/42] example for future extension: mm:gup/writeback: add callbacks for inaccessible pages: source indication Christian Borntraeger 2020-02-17 14:15 ` Ulrich Weigand 2020-02-17 14:38 ` Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 41/42] potential fixup for "s390/mm: provide memory management functions for protected KVM guests" Christian Borntraeger 2020-02-14 22:26 ` [PATCH v2 42/42] KVM: s390: rstify new ioctls in api.rst Christian Borntraeger
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