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

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Date:   Tue, 10 Aug 2021 08:38:46 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jeff Moyer <jmoyer@...hat.com>, dan.j.williams@...el.com
Cc:     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

Jeff,

On Wed, Jul 21 2021 at 15:48, Jeff Moyer wrote:

Please write function names with brackets, i.e. sanitize_phys().

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

[start, end]


> 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?

> 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
         */

> +	end = sanitize_phys(end - 1) + 1;
>  	if (start >= end) {
>  		WARN(1, "%s failed: [mem %#010Lx-%#010Lx], req %s\n", __func__,
>  				start, end - 1, cattr_name(req_type));

Thanks,

        tglx