linux-kernel - Re: [PATCH v2 3/3] arm: extend pfn_valid to take into accound freed memory map alignment

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Message-ID: <YNwbNX7oyosZAuEJ@linux.ibm.com>
Date:   Wed, 30 Jun 2021 10:20:21 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Mike Rapoport <rppt@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-omap@...r.kernel.org, regressions@...ts.linux.dev
Subject: Re: [PATCH v2 3/3] arm: extend pfn_valid to take into accound freed
 memory map alignment

On Tue, Jun 29, 2021 at 03:50:23PM +0300, Mike Rapoport wrote:
> On Tue, Jun 29, 2021 at 02:52:39PM +0300, Tony Lindgren wrote:
> > * Mike Rapoport <rppt@...ux.ibm.com> [210629 10:51]:
> > > 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. 
> > 
> > Yes this allows the system to boot for me :)
> > 
> > I'm still seeing these three prints though:
> > 
> > ...
> > smp: Brought up 1 node, 2 CPUs
> > SMP: Total of 2 processors activated (3994.41 BogoMIPS).
> > CPU: All CPU(s) started in SVC mode.
> > pfn_valid(__pageblock_pfn_to_page+0x14/0xa8): pfn: afe00: is_map: 0 overlaps: 1
> > pfn_valid(__pageblock_pfn_to_page+0x28/0xa8): pfn: affff: is_map: 0 overlaps: 1
> > pfn_valid(__pageblock_pfn_to_page+0x38/0xa8): pfn: afe00: is_map: 0 overlaps: 1
> 
> These pfns do have memory map despite they are stolen in
> arm_memblock_steal():
> 
> memblock_free: [0xaff00000-0xafffffff] arm_memblock_steal+0x50/0x70
> memblock_remove: [0xaff00000-0xafffffff] arm_memblock_steal+0x5c/0x70
> ...
> memblock_free: [0xafe00000-0xafefffff] arm_memblock_steal+0x50/0x70
> memblock_remove: [0xafe00000-0xafefffff] arm_memblock_steal+0x5c/0x70
> 
> But the struct pages there are never initialized.

Actually, with FLATMEM these struct pages will be always set to 0 because
we don't do memory map poisoning with FLATMEM.

I could not find a case where zeroed struct page would cause real trouble,
so I'd say it is more theoretical issue and it can be addressed unrelated
to these changes.

-- 
Sincerely yours,
Mike.