Re: [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 [off-list ref] [210629 05:33]:

quoted

On Mon, Jun 28, 2021 at 06:26:26PM +0300, Tony Lindgren wrote:

quoted

* Mike Rapoport [off-list ref] [210628 14:07]:

quoted

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.

quoted

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

quoted

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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