* Matt Fleming <[email protected]> wrote:
> While _text is currently aligned to PAGE_SIZE in the vmlinux linker
> script because it's based on CONFIG_PHYSICAL_ALIGN, it's always better
> to be explicit about these things to be sure no alignment bugs are
> lurking. There's no analogous enforcement for _end.
>
> Dave provided an example of why the 'npages' calculation is wrong,
>
> "Just for fun, imagine that _end=0xfff and _text=0x1001. npages
> would be 0."
>
> Use PFN_ALIGN() to be sure the calculation is correctly aligned to
> PAGE_SIZE.
>
> Reported-by: Dave Hansen <[email protected]>
> Reported-by: Thomas Gleixner <[email protected]>
> Cc: Borislav Petkov <[email protected]>
> Cc: Sai Praneeth Prakhya <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: <[email protected]>
> Signed-off-by: Matt Fleming <[email protected]>
> ---
> arch/x86/platform/efi/efi_64.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> index a0ac0f9c307f..3a90eb72d153 100644
> --- a/arch/x86/platform/efi/efi_64.c
> +++ b/arch/x86/platform/efi/efi_64.c
> @@ -183,7 +183,7 @@ int __init efi_setup_page_tables(unsigned long pa_memmap,
> unsigned num_pages)
> efi_scratch.phys_stack = virt_to_phys(page_address(page));
> efi_scratch.phys_stack += PAGE_SIZE; /* stack grows down */
>
> - npages = (_end - _text) >> PAGE_SHIFT;
> + npages = (PFN_ALIGN(_end) - PFN_ALIGN(_text)) >> PAGE_SHIFT;
> text = __pa(_text);
Didn't we want to do the _end alignment linker script fix instead?
Alignment assumptions are easy to make when symbols are well aligned typically
(as
in this case), so we should guarantee the alignment property instead of
complicating the code.
Thanks,
Ingo
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