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

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Date:   Fri, 4 May 2018 15:29:16 +0800
From:   joeyli <jlee@...e.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     "Lee, Chun-Yi" <joeyli.kernel@...il.com>,
        linux-efi@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Takashi Iwai <tiwai@...e.de>, Vivek Goyal <vgoyal@...hat.com>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] efi: Fix the size not consistent issue when unmapping
 memory map

Hi Ard,

On Thu, May 03, 2018 at 02:05:51PM +0200, Ard Biesheuvel wrote:
> On 2 May 2018 at 08:17, Lee, Chun-Yi <joeyli.kernel@...il.com> 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);
> >
> > Dave Young's a841aa83d patch fixed kexec issue. On UEFI side, this
> > patch changes the logic in the unmapping function. Using the end
> > address of map to calcuate original size.
> >
> 
> Why do we still need this patch? I.e., in which circumstances will
> efi_memory_map_data::size assume a value that is rounded up or
> otherwise incorrect?
>

There have no other case except kexec. But I think that it's better
to sync mapping/unmapping size between __efi_memmap_init() and 
efi_memmap_unmap(). 


Thanks
Joey Lee
 
> > Thank Randy Wright for his report and testing. And also thank
> > Takashi Iwai for his help to trace issue.
> >
> > Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> > Cc: Takashi Iwai <tiwai@...e.de>
> > Cc: Vivek Goyal <vgoyal@...hat.com>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Tested-by: Randy Wright <rwright@....com>
> > Signed-off-by: "Lee, Chun-Yi" <jlee@...e.com>
> > ---
> >  drivers/firmware/efi/memmap.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/firmware/efi/memmap.c b/drivers/firmware/efi/memmap.c
> > index 5fc7052..1f592d8 100644
> > --- a/drivers/firmware/efi/memmap.c
> > +++ b/drivers/firmware/efi/memmap.c
> > @@ -121,7 +121,7 @@ void __init efi_memmap_unmap(void)
> >         if (!efi.memmap.late) {
> >                 unsigned long size;
> >
> > -               size = efi.memmap.desc_size * efi.memmap.nr_map;
> > +               size = efi.memmap.map_end - efi.memmap.map;
> >                 early_memunmap(efi.memmap.map, size);
> >         } else {
> >                 memunmap(efi.memmap.map);
> > --
> > 2.10.2
> >