linux-kernel - Re: [PATCH] efi: Fix the size not consistent issue when unmapping memory map

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Message-ID: <20180416063414.GG16023@linux-l9pv.suse>
Date:   Mon, 16 Apr 2018 14:34:14 +0800
From:   joeyli <jlee@...e.com>
To:     Dave Young <dyoung@...hat.com>
Cc:     "Lee, Chun-Yi" <joeyli.kernel@...il.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-efi@...r.kernel.org, Takashi Iwai <tiwai@...e.de>,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Randy Wright <rwright@....com>, Ingo Molnar <mingo@...hat.com>,
        akpm@...ux-foundation.org, Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH] efi: Fix the size not consistent issue when unmapping
 memory map

On Mon, Apr 16, 2018 at 10:57:34AM +0800, Dave Young wrote:
> On 04/13/18 at 02:27pm, Lee, Chun-Yi wrote:
> > When using kdump, SOMETIMES the "size not consistent" warning message
> > shows up when the crash kernel boots with early_ioremap_debug parameter:
> > 
> > WARNING: CPU: 0 PID: 0 at ../mm/early_ioremap.c:182 early_iounmap+0x4f/0x12c()
> > early_iounmap(ffffffffff200180, 00000118) [0] size not consistent 00000120
> > 
> > The root cause is that the unmapping size of memory map doesn't
> > match with the original size when mapping:
> > 
> > in __efi_memmap_init()
> > 	map.map = early_memremap(phys_map, data->size);
> > 
> > in efi_memmap_unmap()
> >         size = efi.memmap.desc_size * efi.memmap.nr_map;
> >         early_memunmap(efi.memmap.map, size);
> > 
> > But the efi.memmap.nr_map is from __efi_memmap_init(). The remainder
> > of size was discarded when calculating the nr_map:
> >         map.nr_map = data->size / data->desc_size;
> > 
> > When the original size of memory map region does not equal to the
> > result of multiplication. The "size not consistent" warning
> > will be triggered.
> > 
> > This issue sometimes was hit by kdump because kexec set the efi map
> > size to align with 16 when loading crash kernel image:
> > 
> > in bzImage64_load()
> >         efi_map_sz = efi_get_runtime_map_size();
> >         efi_map_sz = ALIGN(efi_map_sz, 16);
> > 
> > This patch changes the logic in the unmapping function. Using the
> > end address of map to calcuate original size.
> > 
> > Thank Randy Wright for his report and testing. And also thank
> > Takashi Iwai for his help to trace issue.
> 
> Good catch.  The kexec code need to be fixed to use a separate buffer so
> avoid the alignment like what kexec-tools did.  I can submit a fix for
> that.
>

Thanks!
 
> But this issue could be a potential issue even if kexec get fixed so it
> looks worth a fix in efi code as well.  How about mapping only nr_maps
> *desc_size in __efi_memmap_init?  It looks easier to understand.
> 

Takashi has another patch as you said. Finally I sent this patch because
it's smaller.   

Thanks a lot!
Joey Lee