From: Jason Gunthorpe <jgg@ziepe.ca>
To: Matthew Wilcox <willy@infradead.org>
Cc: John Hubbard <jhubbard@nvidia.com>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Dave Hansen <dave.hansen@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
David Rientjes <rientjes@google.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Kees Cook <keescook@chromium.org>, Will Drewry <wad@chromium.org>,
"Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
"Kleen, Andi" <andi.kleen@intel.com>,
Liran Alon <liran.alon@oracle.com>,
Mike Rapoport <rppt@kernel.org>,
x86@kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [RFCv2 08/16] KVM: Use GUP instead of copy_from/to_user() to access guest memory
Date: Mon, 26 Oct 2020 11:16:01 -0300 [thread overview]
Message-ID: <20201026141601.GT36674@ziepe.ca> (raw)
In-Reply-To: <20201026132830.GQ20115@casper.infradead.org>
On Mon, Oct 26, 2020 at 01:28:30PM +0000, Matthew Wilcox wrote:
> > > It's been five years since DAX was merged, and page pinning still
> > > doesn't work. How much longer before the people who are pushing it
> > > realise that it's fundamentally flawed?
> >
> > Is this a separate rant about *only* DAX, or is general RDMA in your sights
> > too? :)
>
> This is a case where it's not RDMA's _fault_ that there's no good API
> for it to do what it needs to do. There's a lot of work needed to wean
> Linux device drivers off their assumption that there's a struct page
> for every byte of memory.
People who care seem to have just given up and are using RDMA ODP, so
I'm not optimistic this DAX issue will ever be solved. I've also
almost removed all the struct page references from this flow in RDMA,
so if there is some way that helps it is certainly doable.
Regardless of DAX the pinning indication is now being used during
fork() for some good reasons, and seems to make sense in other use
cases. It just doesn't seem like a way to solve the DAX issue.
More or less it seems to mean that pages pinned cannot be write
protected and more broadly the kernel should not change the PTEs for
those pages independently of the application. ie the more agressive
COW on fork() caused data corruption regressions...
I wonder if the point here is that some page owners can't/won't
support DMA pinning and should just be blocked completely for them.
I'd much rather have write access pin_user_pages() just fail than oops
the kernel on ext4 owned VMAs, for instance.
Jason
next prev parent reply other threads:[~2020-10-26 14:16 UTC|newest]
Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-20 6:18 [RFCv2 00/16] KVM protected memory extension Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-20 6:18 ` [RFCv2 01/16] x86/mm: Move force_dma_unencrypted() to common code Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-20 6:18 ` [RFCv2 02/16] x86/kvm: Introduce KVM memory protection feature Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-20 6:18 ` [RFCv2 03/16] x86/kvm: Make DMA pages shared Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-20 6:18 ` [RFCv2 04/16] x86/kvm: Use bounce buffers for KVM memory protection Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-20 7:46 ` kernel test robot
2020-10-20 8:48 ` kernel test robot
2020-10-20 6:18 ` [RFCv2 05/16] x86/kvm: Make VirtIO use DMA API in KVM guest Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-20 8:06 ` Christoph Hellwig
2020-10-20 12:47 ` Kirill A. Shutemov
2020-10-20 9:18 ` kernel test robot
2020-10-22 3:31 ` Halil Pasic
2020-10-20 6:18 ` [RFCv2 06/16] x86/kvmclock: Share hvclock memory with the host Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-20 6:18 ` [RFCv2 07/16] x86/realmode: Share trampoline area if KVM memory protection enabled Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-20 6:18 ` [RFCv2 08/16] KVM: Use GUP instead of copy_from/to_user() to access guest memory Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-20 8:25 ` John Hubbard
2020-10-20 12:51 ` Kirill A. Shutemov
2020-10-22 11:49 ` Matthew Wilcox
2020-10-22 19:58 ` John Hubbard
2020-10-26 4:21 ` Matthew Wilcox
2020-10-26 4:44 ` John Hubbard
2020-10-26 13:28 ` Matthew Wilcox
2020-10-26 14:16 ` Jason Gunthorpe [this message]
2020-10-26 20:52 ` John Hubbard
2020-10-20 17:29 ` Ira Weiny
2020-10-22 11:37 ` Kirill A. Shutemov
2020-10-20 6:18 ` [RFCv2 09/16] KVM: mm: Introduce VM_KVM_PROTECTED Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-21 18:47 ` Edgecombe, Rick P
2020-10-22 12:01 ` Kirill A. Shutemov
2020-10-20 6:18 ` [RFCv2 10/16] KVM: x86: Use GUP for page walk instead of __get_user() Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-20 6:18 ` [RFCv2 11/16] KVM: Protected memory extension Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-20 7:17 ` Peter Zijlstra
2020-10-20 12:55 ` Kirill A. Shutemov
2020-10-20 6:18 ` [RFCv2 12/16] KVM: x86: Enabled protected " Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-20 9:01 ` kernel test robot
2020-10-20 6:18 ` [RFCv2 13/16] KVM: Rework copy_to/from_guest() to avoid direct mapping Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-20 9:40 ` kernel test robot
2020-10-20 6:18 ` [RFCv2 14/16] KVM: Handle protected memory in __kvm_map_gfn()/__kvm_unmap_gfn() Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-20 10:34 ` kernel test robot
2020-10-20 11:56 ` kernel test robot
2020-10-21 18:50 ` Edgecombe, Rick P
2020-10-22 12:06 ` Kirill A. Shutemov
2020-10-22 16:59 ` Edgecombe, Rick P
2020-10-23 10:36 ` Kirill A. Shutemov
2020-10-22 3:26 ` Halil Pasic
2020-10-22 12:07 ` Kirill A. Shutemov
2020-10-20 6:18 ` [RFCv2 15/16] KVM: Unmap protected pages from direct mapping Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-20 7:12 ` Peter Zijlstra
2020-10-20 12:18 ` David Hildenbrand
2020-10-20 13:20 ` David Hildenbrand
2020-10-21 1:20 ` Edgecombe, Rick P
2020-10-26 19:55 ` Tom Lendacky
2020-10-21 18:49 ` Edgecombe, Rick P
2020-10-23 12:37 ` Mike Rapoport
2020-10-23 16:32 ` Sean Christopherson
2020-10-20 6:18 ` [RFCv2 16/16] mm: Do not use zero page for VM_KVM_PROTECTED VMAs Kirill A. Shutemov
2020-10-20 6:18 ` Kirill A. Shutemov
2020-10-20 7:46 ` [RFCv2 00/16] KVM protected memory extension Vitaly Kuznetsov
2020-10-20 13:49 ` Kirill A. Shutemov
2020-10-21 14:46 ` Vitaly Kuznetsov
2020-10-23 11:35 ` Kirill A. Shutemov
2020-10-23 12:01 ` Vitaly Kuznetsov
2020-10-21 18:20 ` Andy Lutomirski
2020-10-21 18:20 ` Andy Lutomirski
2020-10-26 15:29 ` Kirill A. Shutemov
2020-10-26 23:58 ` Andy Lutomirski
2020-10-26 23:58 ` Andy Lutomirski
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