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SubjectRe: [PATCH v2 3/3] arm: extend pfn_valid to take into accound freed memory map alignment
Hi,

On Tue, Jun 29, 2021 at 11:54:02AM +0300, Tony Lindgren wrote:
> Hi,
>
> * Mike Rapoport <rppt@linux.ibm.com> [210629 05:33]:
> > On Mon, Jun 28, 2021 at 06:26:26PM +0300, Tony Lindgren wrote:
> > > * Mike Rapoport <rppt@linux.ibm.com> [210628 14:07]:
> > > > Can you please send log with 'memblock=debug' added to the command line?
> > >
> > > Sure, log now available at:
> > >
> > > http://muru.com/beagle-x15.txt
> >
> > Hmm, no clues yet :(
> >
> > Do you have CONFIG_DEBUG_VM, CONFIG_DEBUG_VM_PGFLAGS and
> > CONFIG_PAGE_POISONING enabled in your config?
> > If not, can you please enable them and see if any of VM_BUG_* triggers?
>
> OK enabled, and no errors or warnings are triggered.
>
> > Do you use FLATMEM or SPARSEMEM in your config?
>
> Looks like make omap2plus_defconfig enables FLATMEM:
>
> $ grep -e SPARSEMEM -e FLATMEM .config
> CONFIG_ARCH_FLATMEM_ENABLE=y
> CONFIG_ARCH_SPARSEMEM_ENABLE=y
> CONFIG_FLATMEM_MANUAL=y
> # CONFIG_SPARSEMEM_MANUAL is not set
> CONFIG_FLATMEM=y
>
> > Let's try seeing what PFNs get false results from pfn_valid, maybe this
> > will give a better lead.
>
> With your patch below, system boots with lots of the following:
>
> [ 13.058654] Freeing unused kernel image (initmem) memory: 1024K
> ...
> [ 13.129211] pfn_valid(__sync_icache_dcache+0x2c/0x138): pfn: fffb6: is_map: 1 overlaps: 0
> [ 13.137481] pfn_valid(__sync_icache_dcache+0x2c/0x138): pfn: fffb7: is_map: 1 overlaps: 0

...

> Then changing console loglevel to 0 boots system to login prompt. But I'm
> seeing some init processes segfaulting during start-up.

As it seems, the new version of pfn_valid() decides that last pages are not
valid because of the overflow in memblock_overlaps_region(). As the result,
__sync_icache_dcache() skips flushing these pages.

The patch below should fix this. I've left the prints for now, hopefully
they will not appear anymore.

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 6162a070a410..7ba22d23eca4 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -126,10 +126,16 @@ int pfn_valid(unsigned long pfn)
{
phys_addr_t addr = __pfn_to_phys(pfn);
unsigned long pageblock_size = PAGE_SIZE * pageblock_nr_pages;
+ bool overlaps = memblock_overlaps_region(&memblock.memory,
+ ALIGN_DOWN(addr, pageblock_size),
+ pageblock_size - 1);

if (__phys_to_pfn(addr) != pfn)
return 0;

+ if (memblock_is_map_memory(addr) != overlaps)
+ pr_info("%s(%pS): pfn: %lx: is_map: %d overlaps: %d\n", __func__, (void *)_RET_IP_, pfn, memblock_is_map_memory(addr), overlaps);
+
/*
* If address less than pageblock_size bytes away from a present
* memory chunk there still will be a memory map entry for it
@@ -137,7 +143,7 @@ int pfn_valid(unsigned long pfn)
*/
if (memblock_overlaps_region(&memblock.memory,
ALIGN_DOWN(addr, pageblock_size),
- pageblock_size))
+ pageblock_size - 1))
return 1;

return 0;
--
Sincerely yours,
Mike.

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