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Date: Thu, 5 Nov 2020 13:42:00 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Albert Ou <aou@...s.berkeley.edu>,
Andy Lutomirski <luto@...nel.org>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Borislav Petkov <bp@...en8.de>,
Catalin Marinas <catalin.marinas@....com>,
Christian Borntraeger <borntraeger@...ibm.com>,
Christoph Lameter <cl@...ux.com>,
"David S. Miller" <davem@...emloft.net>,
Dave Hansen <dave.hansen@...ux.intel.com>,
David Hildenbrand <david@...hat.com>,
David Rientjes <rientjes@...gle.com>,
"Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
"H. Peter Anvin" <hpa@...or.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Ingo Molnar <mingo@...hat.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
"Kirill A. Shutemov" <kirill@...temov.name>,
Len Brown <len.brown@...el.com>,
Michael Ellerman <mpe@...erman.id.au>,
Mike Rapoport <rppt@...ux.ibm.com>,
Palmer Dabbelt <palmer@...belt.com>,
Paul Mackerras <paulus@...ba.org>,
Paul Walmsley <paul.walmsley@...ive.com>,
Pavel Machek <pavel@....cz>, Pekka Enberg <penberg@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
Thomas Gleixner <tglx@...utronix.de>,
Vasily Gorbik <gor@...ux.ibm.com>,
Will Deacon <will@...nel.org>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, linux-pm@...r.kernel.org,
linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, sparclinux@...r.kernel.org,
x86@...nel.org
Subject: Re: [PATCH v4 3/4] arch, mm: restore dependency of
__kernel_map_pages() of DEBUG_PAGEALLOC
On Wed, Nov 04, 2020 at 07:02:20PM +0100, Vlastimil Babka wrote:
> On 11/3/20 5:20 PM, Mike Rapoport wrote:
> > From: Mike Rapoport <rppt@...ux.ibm.com>
>
> Subject should have "on DEBUG_PAGEALLOC" ?
>
> > The design of DEBUG_PAGEALLOC presumes that __kernel_map_pages() must never
> > fail. With this assumption is wouldn't be safe to allow general usage of
> > this function.
> >
> > Moreover, some architectures that implement __kernel_map_pages() have this
> > function guarded by #ifdef DEBUG_PAGEALLOC and some refuse to map/unmap
> > pages when page allocation debugging is disabled at runtime.
> >
> > As all the users of __kernel_map_pages() were converted to use
> > debug_pagealloc_map_pages() it is safe to make it available only when
> > DEBUG_PAGEALLOC is set.
> >
> > Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
> > Acked-by: David Hildenbrand <david@...hat.com>
> > Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > ---
> > arch/Kconfig | 3 +++
> > arch/arm64/Kconfig | 4 +---
> > arch/arm64/mm/pageattr.c | 8 ++++++--
> > arch/powerpc/Kconfig | 5 +----
> > arch/riscv/Kconfig | 4 +---
> > arch/riscv/include/asm/pgtable.h | 2 --
> > arch/riscv/mm/pageattr.c | 2 ++
> > arch/s390/Kconfig | 4 +---
> > arch/sparc/Kconfig | 4 +---
> > arch/x86/Kconfig | 4 +---
> > arch/x86/mm/pat/set_memory.c | 2 ++
> > include/linux/mm.h | 10 +++++++---
> > 12 files changed, 26 insertions(+), 26 deletions(-)
> >
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index 56b6ccc0e32d..56d4752b6db6 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -1028,6 +1028,9 @@ config HAVE_STATIC_CALL_INLINE
> > bool
> > depends on HAVE_STATIC_CALL
> > +config ARCH_SUPPORTS_DEBUG_PAGEALLOC
> > + bool
> > +
> > source "kernel/gcov/Kconfig"
> > source "scripts/gcc-plugins/Kconfig"
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index 1d466addb078..a932810cfd90 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -71,6 +71,7 @@ config ARM64
> > select ARCH_USE_QUEUED_RWLOCKS
> > select ARCH_USE_QUEUED_SPINLOCKS
> > select ARCH_USE_SYM_ANNOTATIONS
> > + select ARCH_SUPPORTS_DEBUG_PAGEALLOC
> > select ARCH_SUPPORTS_MEMORY_FAILURE
> > select ARCH_SUPPORTS_SHADOW_CALL_STACK if CC_HAVE_SHADOW_CALL_STACK
> > select ARCH_SUPPORTS_ATOMIC_RMW
> > @@ -1025,9 +1026,6 @@ config HOLES_IN_ZONE
> > source "kernel/Kconfig.hz"
> > -config ARCH_SUPPORTS_DEBUG_PAGEALLOC
> > - def_bool y
> > -
> > config ARCH_SPARSEMEM_ENABLE
> > def_bool y
> > select SPARSEMEM_VMEMMAP_ENABLE
> > diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> > index 1b94f5b82654..439325532be1 100644
> > --- a/arch/arm64/mm/pageattr.c
> > +++ b/arch/arm64/mm/pageattr.c
> > @@ -155,7 +155,7 @@ int set_direct_map_invalid_noflush(struct page *page)
> > .clear_mask = __pgprot(PTE_VALID),
> > };
> > - if (!rodata_full)
> > + if (!debug_pagealloc_enabled() && !rodata_full)
> > return 0;
> > return apply_to_page_range(&init_mm,
> > @@ -170,7 +170,7 @@ int set_direct_map_default_noflush(struct page *page)
> > .clear_mask = __pgprot(PTE_RDONLY),
> > };
> > - if (!rodata_full)
> > + if (!debug_pagealloc_enabled() && !rodata_full)
> > return 0;
> > return apply_to_page_range(&init_mm,
>
> I don't understand these two hunks. Previous patch calls this for
> hibernation when CONFIG_ARCH_HAS_SET_DIRECT_MAP, which is true for arm64.
> Why suddenly this starts to depend on debug_pagealloc_enabled()?
I was confused about this for quite a long :)
On arm64 the changes to direct^w linear map are allowed when
debug_page_alloc() || rodata_full
In hibernation we essentially have now
if (1)
set_direct_map(something)
else
debug_page_alloc_map()
With debug_pagealloc enabled but with rodata_full disabled arm64
versions of set_direct_map_*() will become a nop, so a page that was
unmapped by debug_pagealloc() will not be mapped back.
I'm still puzzled how hibernation might ever need to save a free page,
but that's another story.
--
Sincerely yours,
Mike.
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