linux-kernel - Re: [patch] x86/pat: pass correct address to sanitize

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Date:   Tue, 10 Aug 2021 15:22:19 -0400
From:   Jeff Moyer <jmoyer@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     dan.j.williams@...el.com, Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>,
        Borislav Petkov <bp@...en8.de>, linux-edac@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch] x86/pat: pass correct address to sanitize_phys

Thomas Gleixner <tglx@...utronix.de> writes:

> Jeff,
>
> On Wed, Jul 21 2021 at 15:48, Jeff Moyer wrote:
>
> Please write function names with brackets, i.e. sanitize_phys().

OK, will do.

>> memtype_reserve takes an address range of the form [start, end).  It
>
> [start, end]

Start is inclusive, end is exclusive, so start <= x < end.  I used the
notation found here:

  https://en.wikipedia.org/wiki/Interval_(mathematics)

If that's too confusing, I can stick to inclusive vs exclusive verbiage.

>> then passes the start and end addresses to sanitize_phys, which is meant
>> to operate on the inclusive addresses.  If end falls at the end of the
>> physical address space, sanitize_phys will return 0.  This can result in
>> drivers failing to load:
>>
>> [   10.000087] mpt3sas_cm0: unable to map adapter memory! or resource not found
>> [   10.000334] mpt3sas_cm0: failure at drivers/scsi/mpt3sas/mpt3sas_scsih.c:10597/_scsih_probe()!
>
> Doesn't this trigger the WARN() right below that offending line?

It does.  I'll include the warning message in the v2 posting.

>> Fix this by passing the inclusive end address to sanitize_phys.
>>
>> Fixes: 510ee090abc3 ("x86/mm/pat: Prepare {reserve, free}_memtype() for "decoy" addresses")
>> Signed-off-by: Jeff Moyer <jmoyer@...hat.com>
>> --
>> It might be worth adding a comment, here.  If there are any suggestions
>> on what a sane wording would be, I'm all ears.
>
> See below.
>
>> diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c
>> index 3112ca7786ed..482557905294 100644
>> --- a/arch/x86/mm/pat/memtype.c
>> +++ b/arch/x86/mm/pat/memtype.c
>> @@ -583,7 +583,7 @@ int memtype_reserve(u64 start, u64 end, enum page_cache_mode req_type,
>>  	int err = 0;
>>  
>>  	start = sanitize_phys(start);
>> -	end = sanitize_phys(end);
>
>         /*
>          * [start, end] is an exclusive address range, but
>          * sanitize_phys() expects an inclusive end address
>          */

That works for me (modulo the interval notation), thanks for the
suggestion.

Thanks!
Jeff