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

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Date:   Tue, 28 Feb 2017 16:34:39 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     <linux-arch@...r.kernel.org>, <linux-efi@...r.kernel.org>,
        <kvm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        <kasan-dev@...glegroups.com>, <linux-mm@...ck.org>,
        <iommu@...ts.linux-foundation.org>, Rik van Riel <riel@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Larry Woodman <lwoodman@...hat.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v4 11/28] x86: Add support to determine the E820 type
 of an address

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@....com>
>> ---
>>  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,
>