Re: [PATCH v2 1/2] mm: fix the pfn calculation mistake in __ioremap_check_ram

From: Thomas Gleixner
Date: Sat Jun 19 2021 - 17:45:22 EST


Yaohui!

On Fri, Jun 11 2021 at 12:21, Yaohui Wang wrote:

A few formal things upfront. The prefix of the subject is incorrect. It
should be "x86/ioremap:" git log $FILE helps to figure that out.

Looking at the Signed-off-by chain below this misses either a

From: Ben Luo <luoben@xxxxxxxxxxxxxxxxx>

right at the top of the changelog or a Co-Developed-by tag. See
Documentation/process/

> In arch/x86/mm/ioremap.c:__ioremap_check_ram, the original pfn
> wrapping

Just "In __ioremap_check_ram() ..." please. The file name is
uninteresting and we want the '()' at the end of the symbol so it's
obvious that this is a function.

> calculation may cause the pfn range to ignore the very start page, if
> res->start is not page-aligned, or the very end page, if res->end is not
> page aligned.
>
> So start_pfn should wrap down the res->start address, and end_pfn should
> wrap up the res->end address. This makes the pfn range completely
> contain [res->start, res->end] ram range. This check is more strict and is
> more reasonable.

This lacks a "Fixes:" tag

> Signed-off-by: Ben Luo <luoben@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Yahui Wang <yaohuiwang@xxxxxxxxxxxxxxxxx>
> ---
> arch/x86/mm/ioremap.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
> index 9e5ccc56f..79adf0d2d 100644
> --- a/arch/x86/mm/ioremap.c
> +++ b/arch/x86/mm/ioremap.c
> @@ -74,8 +74,8 @@ static unsigned int __ioremap_check_ram(struct resource *res)
> if ((res->flags & IORESOURCE_SYSTEM_RAM) != IORESOURCE_SYSTEM_RAM)
> return 0;
>
> - start_pfn = (res->start + PAGE_SIZE - 1) >> PAGE_SHIFT;
> - stop_pfn = (res->end + 1) >> PAGE_SHIFT;
> + start_pfn = res->start >> PAGE_SHIFT;
> + stop_pfn = (res->end + PAGE_SIZE) >> PAGE_SHIFT;

Please make that:

start_pfn = PFN_DOWN(res->start);
stop_pfn = PFN_UP(res->end);

which gives you the first and the last PFN of that range. That obviously
requires to fix the below as well, but that code is unreadable anyway.

> if (stop_pfn > start_pfn) {
> for (i = 0; i < (stop_pfn - start_pfn); ++i)
> if (pfn_valid(start_pfn + i) &&

npages = stop_pfn - start_pfn + 1;
for (i = 0; i < npages; i++) {
if (.....)
}

you get the idea, right?

Thanks,

tglx