Re: [RFC PATCH v4 11/28] x86: Add support to determine the E820 type of an address

[Tom Lendacky]

On 2/20/2017 2:09 PM, Borislav Petkov wrote:
> On Thu, Feb 16, 2017 at 09:44:30AM -0600, Tom Lendacky wrote:
> > This patch adds support to return the E820 type associated with an address
>
> s/This patch adds/Add/
>
> > range.
> >
> > Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> > ---
> >  arch/x86/include/asm/e820/api.h   |    2 ++
> >  arch/x86/include/asm/e820/types.h |    2 ++
> >  arch/x86/kernel/e820.c            |   26 +++++++++++++++++++++++---
> >  3 files changed, 27 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/e820/api.h b/arch/x86/include/asm/e820/api.h
> > index 8e0f8b8..7c1bdc9 100644
> > --- a/arch/x86/include/asm/e820/api.h
> > +++ b/arch/x86/include/asm/e820/api.h
> > @@ -38,6 +38,8 @@
> >  extern void e820__reallocate_tables(void);
> >  extern void e820__register_nosave_regions(unsigned long limit_pfn);
> >
> > +extern enum e820_type e820__get_entry_type(u64 start, u64 end);
> > +
> >  /*
> >   * Returns true iff the specified range [start,end) is completely contained inside
> >   * the ISA region.
> > diff --git a/arch/x86/include/asm/e820/types.h b/arch/x86/include/asm/e820/types.h
> > index 4adeed0..bf49591 100644
> > --- a/arch/x86/include/asm/e820/types.h
> > +++ b/arch/x86/include/asm/e820/types.h
> > @@ -7,6 +7,8 @@
> >   * These are the E820 types known to the kernel:
> >   */
> >  enum e820_type {
> > +	E820_TYPE_INVALID	= 0,
> > +
>
> Now this is strange - ACPI spec doesn't explicitly say that range type 0
> is invalid. Am I looking at the wrong place?
>
> "Table 15-312 Address Range Types12" in ACPI spec 6.
>
> If 0 is really the invalid entry, then e820_print_type() needs updating
> too. And then the invalid-entry-add should be a separate patch.

The 0 return (originally) was to indicate that an e820 entry for the
range wasn't found. This series just gave it a name.  So it's not that
the type field held a 0.  Since 0 isn't defined in the ACPI spec I don't
see an issue with creating it and I can add a comment to the effect that
this value is used for the type when an e820 entry isn't found. I could
always rename it to E820_TYPE_NOT_FOUND if that would help.

Or if we want to guard against ACPI adding a type 0 in the future, I
could make the function return an int and then return -EINVAL if an e820
entry isn't found.  This might be the better option.

Thanks,
Tom


> >  	E820_TYPE_RAM		= 1,
> >  	E820_TYPE_RESERVED	= 2,
> >  	E820_TYPE_ACPI		= 3,