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From: David Hildenbrand <david@redhat.com>
To: Mike Rapoport <rppt@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>,
	Andy Lutomirski <luto@kernel.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Borislav Petkov <bp@alien8.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Christoph Lameter <cl@linux.com>,
	"David S. Miller" <davem@davemloft.net>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	David Rientjes <rientjes@google.com>,
	"Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Heiko Carstens <hca@linux.ibm.com>,
	Ingo Molnar <mingo@redhat.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Len Brown <len.brown@intel.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Mackerras <paulus@samba.org>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Pavel Machek <pavel@ucw.cz>, Pekka Enberg <penberg@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Vasily Gorbik <gor@linux.ibm.com>, Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-pm@vger.kernel.org, linux-riscv@lists.infradead.org,
	linux-s390@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	sparclinux@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH 0/4] arch, mm: improve robustness of direct map manipulation
Date: Thu, 29 Oct 2020 09:15:47 +0100	[thread overview]
Message-ID: <30075bb8-caed-c4de-c09e-e0f6fb964a8d@redhat.com> (raw)
In-Reply-To: <20201025101555.3057-1-rppt@kernel.org>

On 25.10.20 11:15, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> Hi,
> 
> During recent discussion about KVM protected memory, David raised a concern
> about usage of __kernel_map_pages() outside of DEBUG_PAGEALLOC scope [1].
> 
> Indeed, for architectures that define CONFIG_ARCH_HAS_SET_DIRECT_MAP it is
> possible that __kernel_map_pages() would fail, but since this function is
> void, the failure will go unnoticed.
> 
> Moreover, there's lack of consistency of __kernel_map_pages() semantics
> across architectures as some guard this function with
> #ifdef DEBUG_PAGEALLOC, some refuse to update the direct map if page
> allocation debugging is disabled at run time and some allow modifying the
> direct map regardless of DEBUG_PAGEALLOC settings.
> 
> This set straightens this out by restoring dependency of
> __kernel_map_pages() on DEBUG_PAGEALLOC and updating the call sites
> accordingly.
> 

So, I was primarily wondering if we really have to touch direct mappings 
in hibernation code, or if we can avoid doing that. I was wondering if 
we cannot simply do something like kmap() when trying to access a 
!mapped page. Similar to reading old-os memory after kexec when in 
kdump. Just a thought.

-- 
Thanks,

David / dhildenb



      parent reply	other threads:[~2020-10-29  8:16 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-25 10:15 [PATCH 0/4] arch, mm: improve robustness of direct map manipulation Mike Rapoport
2020-10-25 10:15 ` [PATCH 1/4] mm: introduce debug_pagealloc_map_pages() helper Mike Rapoport
2020-10-26 11:05   ` David Hildenbrand
2020-10-26 11:54     ` Mike Rapoport
2020-10-26 11:55       ` David Hildenbrand
2020-10-25 10:15 ` [PATCH 2/4] PM: hibernate: improve robustness of mapping pages in the direct map Mike Rapoport
2020-10-26  0:38   ` Edgecombe, Rick P
2020-10-26  9:15     ` Mike Rapoport
2020-10-26 18:57       ` Edgecombe, Rick P
2020-10-27  8:49         ` Mike Rapoport
2020-10-27 22:44           ` Edgecombe, Rick P
2020-10-28  9:41             ` Mike Rapoport
2020-10-27  1:10       ` Edgecombe, Rick P
2020-10-28 21:15   ` Edgecombe, Rick P
2020-10-29  7:54     ` Mike Rapoport
2020-10-29 23:19       ` Edgecombe, Rick P
2020-11-01 17:02         ` Mike Rapoport
2020-10-25 10:15 ` [PATCH 3/4] arch, mm: restore dependency of __kernel_map_pages() of DEBUG_PAGEALLOC Mike Rapoport
2020-10-25 10:15 ` [PATCH 4/4] arch, mm: make kernel_page_present() always available Mike Rapoport
2020-10-26  0:54   ` Edgecombe, Rick P
2020-10-26  9:31     ` Mike Rapoport
2020-10-26  1:13 ` [PATCH 0/4] arch, mm: improve robustness of direct map manipulation Edgecombe, Rick P
2020-10-26  9:05   ` Mike Rapoport
2020-10-26 18:05     ` Edgecombe, Rick P
2020-10-27  8:38       ` Mike Rapoport
2020-10-27  8:46         ` David Hildenbrand
2020-10-27  9:47           ` Mike Rapoport
2020-10-27 10:34             ` David Hildenbrand
2020-10-28 11:09           ` Mike Rapoport
2020-10-28 11:17             ` David Hildenbrand
2020-10-28 12:22               ` Mike Rapoport
2020-10-28 18:31             ` Edgecombe, Rick P
2020-10-28 11:20         ` Will Deacon
2020-10-28 11:30           ` Mike Rapoport
2020-10-28 21:03             ` Edgecombe, Rick P
2020-10-29  8:12               ` Mike Rapoport
2020-10-29 23:19                 ` Edgecombe, Rick P
2020-10-29  8:15 ` David Hildenbrand [this message]

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