Re: [PATCH v2 1/5] x86/mm/pageattr: Ensure cpa->pfn only contains page frame numbers

[Matt Fleming]

On Wed, 18 Nov, at 09:14:23AM, Ingo Molnar wrote:
> 
> * Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx> wrote:
> 
> > > > +	npages = (_end - _text) >> PAGE_SHIFT;
> > > 
> > > You really need to PFN_ALIGN _end and _text. Has been wrong in the
> > > existing code as well.
> >  
> > Hmm... very good point.
> 
> So I think we should instead guarantee that _end and _text are page aligned.
> 
> _text is already page aligned:
> 
> SECTIONS
> {
> #ifdef CONFIG_X86_32
>         . = LOAD_OFFSET + LOAD_PHYSICAL_ADDR;
>         phys_startup_32 = startup_32 - LOAD_OFFSET;
> #else
>         . = __START_KERNEL;
>         phys_startup_64 = startup_64 - LOAD_OFFSET;
> #endif
> 
>         /* Text and read-only data */
>         .text :  AT(ADDR(.text) - LOAD_OFFSET) {
>                 _text = .;
> 
> The reason for aligning _end as well is that we already page-align the BSS and BRK 
> sections of the kernel and its various section boundary symbols:
> 
>         /* BSS */
>         . = ALIGN(PAGE_SIZE);
>         .bss : AT(ADDR(.bss) - LOAD_OFFSET) {
>                 __bss_start = .;
>                 *(.bss..page_aligned)
>                 *(.bss)
>                 . = ALIGN(PAGE_SIZE);
>                 __bss_stop = .;
>         }
> 
>         . = ALIGN(PAGE_SIZE);
>         .brk : AT(ADDR(.brk) - LOAD_OFFSET) {
>                 __brk_base = .;
>                 . += 64 * 1024;         /* 64k alignment slop space */
>                 *(.brk_reservation)     /* areas brk users have reserved */
>                 __brk_limit = .;
>         }
> 
>         _end = .;
> 
>         STABS_DEBUG
>         DWARF_DEBUG
> 
> _end is the only odd one out, so we should align it as well - because it's easy to 
> make such pfn conversion bugs.

FWIW, I saw no changes in either 32-bit or 64-bit vmlinux size when
building with the following patch, so it seems like a pretty easy win,

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