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From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Baoquan He <bhe@redhat.com>
Cc: tglx@linutronix.de, mingo@kernel.org, hpa@zytor.com,
	thgarnie@google.com, kirill.shutemov@linux.intel.com,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] x86/mm/KASLR: Adjust the vmemmap size according to paging mode
Date: Wed, 29 Aug 2018 15:05:30 +0300	[thread overview]
Message-ID: <20180829120530.6dhgsautjjrj4ztt@kshutemo-mobl1> (raw)
In-Reply-To: <20180829021754.21850-2-bhe@redhat.com>

On Wed, Aug 29, 2018 at 10:17:54AM +0800, Baoquan He wrote:
> Vmemmap area has different base and size depending on paging mode.
> Now we just hardcode its size as 1TB in memory KASLR, it's not
> right for 5-level paging mode.
> 
> Adjust it according to paging mode and use it during memory KASLR.
> 

I think 512TiB is wasteful for 5-level paging. We don't need that much.

1TiB limit with 4-level paging is required to fit struct pages for all
64TiB of physical memory, assuming each struct page is 64 bytes.

With 5-level paging the limit on physical memory is not 512-times bigger:
we cap at 52-bit physical address space. So it's just 64 times bigger and
we need only 64TiB in worst case.

I think we can limit it further by taking into account memory_tb. Most of
machines will be fine with 1TiB there and we save few more bits from
KASLR.

-- 
 Kirill A. Shutemov

  reply	other threads:[~2018-08-29 12:05 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-29  2:17 [PATCH 1/2] x86/mm/KASLR: Fix the wrong calculation of kalsr region initial size Baoquan He
2018-08-29  2:17 ` [PATCH 2/2] x86/mm/KASLR: Adjust the vmemmap size according to paging mode Baoquan He
2018-08-29 12:05   ` Kirill A. Shutemov [this message]
2018-08-29 12:16     ` Baoquan He
2018-08-29 12:18     ` Baoquan He
2018-08-29 12:26       ` Kirill A. Shutemov
2018-08-29 12:51         ` Baoquan He
2018-08-30 15:25     ` Baoquan He
2018-09-02 20:52       ` Kirill A. Shutemov
2018-09-03  7:47         ` Baoquan He
2018-09-03 10:26           ` Kirill A. Shutemov
2018-09-03 14:52             ` Baoquan He
2018-09-04  8:13               ` Kirill A. Shutemov
2018-09-05  8:15                 ` Baoquan He
2018-09-05 12:09                   ` Kirill A. Shutemov
2018-09-05 12:37                     ` Baoquan He
2018-08-29 11:49 ` [PATCH 1/2] x86/mm/KASLR: Fix the wrong calculation of kalsr region initial size Kirill A. Shutemov
2018-09-04 17:57   ` Thomas Garnier
2018-09-08 12:10 ` Thomas Gleixner
2018-09-08 13:33   ` Baoquan He

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