linux-kernel - Re: [PATCH v5 6/6] mtrr, mm, x86: Enhance MTRR checks for KVA huge page mapping

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150518190150.GC23618@pd.tnic>
Date:	Mon, 18 May 2015 21:01:50 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Toshi Kani <toshi.kani@...com>
Cc:	akpm@...ux-foundation.org, hpa@...or.com, tglx@...utronix.de,
	mingo@...hat.com, linux-mm@...ck.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, dave.hansen@...el.com,
	Elliott@...com, pebolle@...cali.nl, mcgrof@...e.com
Subject: Re: [PATCH v5 6/6] mtrr, mm, x86: Enhance MTRR checks for KVA huge
 page mapping

On Mon, May 18, 2015 at 11:22:39AM -0600, Toshi Kani wrote:
> > diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
> > index c30f9819786b..f1894daa79ee 100644
> > --- a/arch/x86/mm/pgtable.c
> > +++ b/arch/x86/mm/pgtable.c
> > @@ -566,19 +566,24 @@ void native_set_fixmap(enum fixed_addresses idx, phys_addr_t phys,
> >  /**
> >   * pud_set_huge - setup kernel PUD mapping
> >   *
> > - * MTRR can override PAT memory types with 4KiB granularity.  Therefore,
> > - * this function does not set up a huge page when the range is covered
> > - * by a non-WB type of MTRR.  MTRR_TYPE_INVALID indicates that MTRR are
> > - * disabled.
> > + * MTRRs can override PAT memory types with 4KiB granularity. Therefore,
> > + * this function sets up a huge page only if all of the following
> > + * conditions are met:
> 
> It should be "if any of the following condition is met".  Or, does NOT
> setup if all of ...
> 
> > + *
> > + *  - MTRRs are disabled.
> > + *  - The range is mapped uniformly by an MTRR, i.e. the range is
> > + *    fully covered by a single MTRR entry or the default type.
> > + *  - The MTRR memory type is WB.

Hmm, ok, so this is kinda like "any" but they also depend on each other.
So it is

If
	- MTRRs are disabled

	or

	- MTRRs are enabled and the range is completely covered by a single MTRR

	or

	 - MTRRs are enabled and the range is not completely covered by a
	 single MTRR but the memory type of the range is WB, even if covered by
	 multiple MTRRs.

Right?

So tell me this: why do we need to repeat that over those KVA helpers?
It's not like the callers can do anything about it, can they?

So maybe that comment - expanded into more detail - should be over
mtrr_type_lookup() only. That'll be better, methinks.

Hmm.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/