Subject: Re: [PATCH 3/3] arm: extend pfn_valid to take into accound freed memory map alignment

From: Mike Rapoport <[email-masked]>
Date: Tue, 18 May 2021 18:52:49 +0300

On Tue, May 18, 2021 at 08:49:43PM +0800, Kefeng Wang wrote:
> 
> 
> On 2021/5/18 17:06, Mike Rapoport wrote:
> > From: Mike Rapoport <[email-masked]>
> > 
> > When unused memory map is freed the preserved part of the memory map is
> > extended to match pageblock boundaries because lots of core mm
> > functionality relies on homogeneity of the memory map within pageblock
> > boundaries.
> > 
> > Since pfn_valid() is used to check whether there is a valid memory map
> > entry for a PFN, make it return true also for PFNs that have memory map
> > entries even if there is no actual memory populated there.
> > 
> > Signed-off-by: Mike Rapoport <[email-masked]>
> > ---
> >   arch/arm/mm/init.c | 15 ++++++++++++++-
> >   1 file changed, 14 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> > index 9d4744a632c6..bb678c0ba143 100644
> > --- a/arch/arm/mm/init.c
> > +++ b/arch/arm/mm/init.c
> > @@ -125,11 +125,24 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max_low,
> >   int pfn_valid(unsigned long pfn)
> >   {
> >   	phys_addr_t addr = __pfn_to_phys(pfn);
> > +	unsigned long pageblock_size = PAGE_SIZE * pageblock_nr_pages;
> >   	if (__phys_to_pfn(addr) != pfn)
> >   		return 0;
> > -	return memblock_is_map_memory(addr);
> > +	if (memblock_is_map_memory(addr))
> > +		return 1;
> > +
> > +	/*
> > +	 * If address less than pageblock_size bytes away from a present
> > +	 * memory chunk there still will be a memory map entry for it
> > +	 * because we round freed memory map to the pageblock boundaries
> > +	 */
> > +	if (memblock_is_map_memory(ALIGN(addr + 1, pageblock_size)) ||
> > +	    memblock_is_map_memory(ALIGN_DOWN(addr, pageblock_size)))
> > +		return 1;
> 
> Hi Mike, with patch3, the system won't boot.

Hmm, apparently I've miscalculated the ranges...

Can you please check with the below patch on top of this series:

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index bb678c0ba143..2fafbbc8e73b 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -138,8 +138,9 @@ int pfn_valid(unsigned long pfn)
 	 * memory chunk there still will be a memory map entry for it
 	 * because we round freed memory map to the pageblock boundaries
 	 */
-	if (memblock_is_map_memory(ALIGN(addr + 1, pageblock_size)) ||
-	    memblock_is_map_memory(ALIGN_DOWN(addr, pageblock_size)))
+	if (memblock_overlaps_region(&memblock.memory,
+				     ALIGN_DOWN(addr, pageblock_size),
+				     pageblock_size);
 		return 1;
 
 	return 0;

-- 
Sincerely yours,
Mike.

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