From: David Hildenbrand <david@redhat.com>
To: "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>,
Mike Rapoport <rppt@linux.ibm.com>
Cc: 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 15/16] KVM: Unmap protected pages from direct mapping
Date: Tue, 20 Oct 2020 15:20:13 +0200 [thread overview]
Message-ID: <2759b4bf-e1e3-d006-7d86-78a40348269d@redhat.com> (raw)
In-Reply-To: <f153ef1a-a758-dec7-b39c-9990aac9d653@redhat.com>
On 20.10.20 14:18, David Hildenbrand wrote:
> On 20.10.20 08:18, Kirill A. Shutemov wrote:
>> If the protected memory feature enabled, unmap guest memory from
>> kernel's direct mappings.
>
> Gah, ugly. I guess this also defeats compaction, swapping, ... oh gosh.
> As if all of the encrypted VM implementations didn't bring us enough
> ugliness already (SEV extensions also don't support reboots, but can at
> least kexec() IIRC).
>
> Something similar is done with secretmem [1]. And people don't seem to
> like fragmenting the direct mapping (including me).
>
> [1] https://lkml.kernel.org/r/20200924132904.1391-1-rppt@kernel.org
>
I just thought "hey, we might have to replace pud/pmd mappings by page
tables when calling kernel_map_pages", this can fail with -ENOMEM, why
isn't there proper error handling.
Then I dived into __kernel_map_pages() which states:
"The return value is ignored as the calls cannot fail. Large pages for
identity mappings are not used at boot time and hence no memory
allocations during large page split."
I am probably missing something important, but how is calling
kernel_map_pages() safe *after* booting?! I know we use it for
debug_pagealloc(), but using it in a production-ready feature feels
completely irresponsible. What am I missing?
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2020-10-20 13:20 UTC|newest]
Thread overview: 57+ 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 ` [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 [this message]
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
2020-10-26 23:58 ` Andy Lutomirski
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