linux-kernel - Re: [PATCH] X86: MM: Add PAT Type write-through in combination with mtrr

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: <20131028112505.GD2278@thinkpad.fritz.box>
Date:	Mon, 28 Oct 2013 12:25:05 +0100
From:	Andreas Werner <wernerandy@....de>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Ingo Molnar <mingo@...nel.org>, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org,
	dave@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] X86: MM: Add PAT Type write-through in combination with
 mtrr

On Mon, Oct 28, 2013 at 11:57:31AM +0100, Borislav Petkov wrote:
> On Mon, Oct 28, 2013 at 11:34:28AM +0100, Andreas Werner wrote:
> > Yes the reads are only for packet data, the commands or configuration
> > registers are mapped non cachable.
> > 
> > I´ve tried WB, but on PCIe Tracer i could not see any burst access.
> > Thats the reason why i have created this patch.
> > 
> > Is there a chance to get this patch into the kernel? Or
> > is this solution so special?
> 
> Ok, but your patch returns WB pat type for WT MTRR type, AFAICT.
> 
> You want to do:
> 
>   PAT=Write-Back + MTRR=Write-Through = Effective Memory of Write-Through
>
Yes thats right.
 
> but you end up doing
> 
>   PAT=Write-Back + MTRR=Write-Through = Effective Memory of Write-Back
>
No the effective memory type is WT, check out the Intel document with the
table of Effective memory type combinations.
 
> What am I missing or misunderstanding?
> 
> AFAICT, you want to return _PAGE_PWT for MTRR_TYPE_WRTHROUGH, no?

Yes but, there is no way in the kernel to mark a memory WT,
there is just ioremap_wc for Write combining and ioremap_cache
for Write Back, and as you can see in the Intel Effective Memory type
table, if you combine PAT=WB and MTRR=WT you will get a effective memory
of WT.

regards 
Andy
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> Sent from a fat crate under my desk. Formatting is fine.
> --
--
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/