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From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Andy Lutomirski <luto@amacapital.net>
Cc: 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 ML <x86@kernel.org>,
	kvm list <kvm@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [RFCv2 00/16] KVM protected memory extension
Date: Mon, 26 Oct 2020 18:29:10 +0300	[thread overview]
Message-ID: <20201026152910.happu7wic4qjxmp7@box> (raw)
In-Reply-To: <CALCETrXn_ghtLK34jmKSSp5_SF6hh5GOfBLKdxXgp5ZTbN8uEA@mail.gmail.com>

On Wed, Oct 21, 2020 at 11:20:56AM -0700, Andy Lutomirski wrote:
> > On Oct 19, 2020, at 11:19 PM, Kirill A. Shutemov <kirill@shutemov.name> wrote:
> 
> > For removing the userspace mapping, use a trick similar to what NUMA
> > balancing does: convert memory that belongs to KVM memory slots to
> > PROT_NONE: all existing entries converted to PROT_NONE with mprotect() and
> > the newly faulted in pages get PROT_NONE from the updated vm_page_prot.
> > The new VMA flag -- VM_KVM_PROTECTED -- indicates that the pages in the
> > VMA must be treated in a special way in the GUP and fault paths. The flag
> > allows GUP to return the page even though it is mapped with PROT_NONE, but
> > only if the new GUP flag -- FOLL_KVM -- is specified. Any userspace access
> > to the memory would result in SIGBUS. Any GUP access without FOLL_KVM
> > would result in -EFAULT.
> >
> 
> I definitely like the direction this patchset is going in, and I think
> that allowing KVM guests to have memory that is inaccessible to QEMU
> is a great idea.
> 
> I do wonder, though: do we really want to do this with these PROT_NONE
> tricks, or should we actually come up with a way to have KVM guest map
> memory that isn't mapped into QEMU's mm_struct at all?  As an example
> of the latter, I mean something a bit like this:
> 
> https://lkml.kernel.org/r/CALCETrUSUp_7svg8EHNTk3nQ0x9sdzMCU=h8G-Sy6=SODq5GHg@mail.gmail.com
> 
> I don't mean to say that this is a requirement of any kind of
> protected memory like this, but I do think we should understand the
> tradeoffs, in terms of what a full implementation looks like, the
> effort and time frames involved, and the maintenance burden of
> supporting whatever gets merged going forward.

I considered the PROT_NONE trick neat. Complete removing of the mapping
from QEMU would require more changes into KVM and I'm not really familiar
with it.

About tradeoffs: the trick interferes with AutoNUMA. I didn't put much
thought into how we can get it work together. Need to look into it.

Do you see other tradeoffs?

-- 
 Kirill A. Shutemov


  reply	other threads:[~2020-10-26 15:29 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
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 ` [RFCv2 02/16] x86/kvm: Introduce KVM memory protection feature 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 ` [RFCv2 04/16] x86/kvm: Use bounce buffers for KVM memory protection Kirill A. Shutemov
2020-10-20  6:18 ` [RFCv2 05/16] x86/kvm: Make VirtIO use DMA API in KVM guest Kirill A. Shutemov
2020-10-20  8:06   ` Christoph Hellwig
2020-10-20 12:47     ` Kirill A. Shutemov
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 ` [RFCv2 07/16] x86/realmode: Share trampoline area if KVM memory protection enabled 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  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
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
2020-10-21 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 ` [RFCv2 11/16] KVM: Protected memory extension 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 ` [RFCv2 13/16] KVM: Rework copy_to/from_guest() to avoid direct mapping Kirill A. Shutemov
2020-10-20  6:18 ` [RFCv2 14/16] KVM: Handle protected memory in __kvm_map_gfn()/__kvm_unmap_gfn() Kirill A. Shutemov
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  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  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
2020-10-26 15:29   ` Kirill A. Shutemov [this message]
2020-10-26 23:58     ` Andy Lutomirski

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