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From: Joerg Roedel <jroedel@suse.de>
To: Andy Lutomirski <luto@kernel.org>
Cc: David Rientjes <rientjes@google.com>,
	Borislav Petkov <bp@alien8.de>,
	Sean Christopherson <seanjc@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Andi Kleen <ak@linux.intel.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Jon Grimm <jon.grimm@amd.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Ingo Molnar <mingo@redhat.com>,
	"Kaplan, David" <David.Kaplan@amd.com>,
	Varad Gautam <varad.gautam@suse.com>,
	Dario Faggioli <dfaggioli@suse.com>,
	x86@kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev
Subject: Re: Runtime Memory Validation in Intel-TDX and AMD-SNP
Date: Tue, 20 Jul 2021 10:44:24 +0200	[thread overview]
Message-ID: <YPaM6G4Wt/V6QZy+@suse.de> (raw)
In-Reply-To: <a5ac5af6-7e28-4e9c-e55b-db31842a5911@kernel.org>

On Mon, Jul 19, 2021 at 05:26:20PM -0700, Andy Lutomirski wrote:
> At the risk of asking a potentially silly question, would it be
> reasonable to treat non-validated memory as not-present for kernel
> purposes and hot-add it in a thread as it gets validated?  Or would this
> result in poor system behavior before enough memory is validated?
> Perhaps we should block instead of failing allocations if we want more
> memory than is currently validated?

That is basically the idea of pre-validating the first X GB of memory
(X==4 has been proposed) and validate the rest at runtime. I see two
problems with this:

	1) Pre-validating large amounts of memory takes a lot of time
	   (in the range of a few seconds). This is not suitable for all
	   workloads like, e.g., containers which want to boot in a few
	   hundred milliseconds.

	2) It limits the physical address range for KASLR placement,
	   factually reducing the randomness of where the kernel is
	   placed in physical memory.

With the proposal I sent here only enough memory for the boot-loader and
the kernel image is pre-validated, and when the decompressor takes over
it can place the kernel anywhere, even in yet unvalidated/unaccepted
memory.

Regards,

	Joerg

  parent reply	other threads:[~2021-07-20  8:44 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-19 12:58 Runtime Memory Validation in Intel-TDX and AMD-SNP Joerg Roedel
2021-07-19 13:07 ` Matthew Wilcox
2021-07-19 15:02   ` Joerg Roedel
2021-07-19 20:39 ` Andi Kleen
2021-07-20  8:55   ` Joerg Roedel
2021-07-20  9:34     ` Dr. David Alan Gilbert
2021-07-20 11:50       ` Joerg Roedel
2021-07-20  0:26 ` Andy Lutomirski
2021-07-20  1:51   ` Erdem Aktas
2021-07-20  2:00     ` Erdem Aktas
2021-07-20  3:30     ` Andy Lutomirski
2021-07-20 19:54       ` Erdem Aktas
2021-07-20 22:01         ` Andi Kleen
2021-07-20 23:55           ` Erdem Aktas
2021-07-21  0:35             ` Andi Kleen
2021-07-21  8:51           ` Joerg Roedel
2021-07-20  5:17     ` Andi Kleen
2021-07-20  9:11       ` Joerg Roedel
2021-07-20 17:32         ` Andi Kleen
2021-07-20 23:09       ` Erdem Aktas
2021-07-21  0:38         ` Andi Kleen
2021-07-22 17:31       ` Marc Orr
2021-07-26 18:55         ` Joerg Roedel
2021-07-20  8:44   ` Joerg Roedel [this message]
2021-07-20 14:14   ` Dave Hansen
2021-07-20 17:30 ` Kirill A. Shutemov
2021-07-21  9:20   ` Mike Rapoport
2021-07-21 10:02     ` Kirill A. Shutemov
2021-07-21 10:22       ` Mike Rapoport
2021-07-21 10:53       ` Joerg Roedel
2021-07-21  9:25   ` Joerg Roedel
2021-07-21 10:25     ` Kirill A. Shutemov
2021-07-21 10:48       ` Joerg Roedel
2021-07-22 15:46   ` David Hildenbrand
2021-07-26 19:02     ` Joerg Roedel
2021-07-27  9:34       ` David Hildenbrand
2021-08-02 10:19         ` Joerg Roedel
2021-08-02 18:47           ` David Hildenbrand
2021-07-22 15:57 ` David Hildenbrand
2021-07-22 19:51 ` Kirill A. Shutemov
2021-07-23 15:23   ` Mike Rapoport
2021-07-23 16:29     ` Kirill A. Shutemov
2021-07-25  9:16       ` Mike Rapoport
2021-07-25 18:28         ` Kirill A. Shutemov
2021-07-26 10:00           ` Mike Rapoport
2021-07-26 11:53             ` Kirill A. Shutemov
2021-07-26 19:13   ` Joerg Roedel
2021-07-26 23:02   ` Erdem Aktas
2021-07-26 23:54     ` Kirill A. Shutemov
2021-07-27  1:35       ` Erdem Aktas
2021-07-23 11:04 ` Varad Gautam
2021-07-23 14:34   ` Kaplan, David

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