linux-kernel - Re: [PATCH v6 26/34] iommu/amd: Allow the AMD IOMMU to work with memory encryption

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: <20170615094111.wga334kg2bhxqib3@pd.tnic>
Date:   Thu, 15 Jun 2017 11:41:12 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     linux-arch@...r.kernel.org, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.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>,
        Larry Woodman <lwoodman@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dave Young <dyoung@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v6 26/34] iommu/amd: Allow the AMD IOMMU to work with
 memory encryption

On Wed, Jun 14, 2017 at 03:40:28PM -0500, Tom Lendacky wrote:
> I was trying to keep all the logic for it here in the SME related files
> rather than put it in the iommu code itself. But it is easy enough to
> move if you think it's worth it.

Yes please - the less needlessly global symbols, the better.

> > Also, you said in another mail on this subthread that c->microcode
> > is not yet set. Are you saying, that the iommu init gunk runs before
> > init_amd(), where we do set c->microcode?
> > 
> > If so, we can move the setting to early_init_amd() or so.
> 
> I'll look into that.

And I don't think c->microcode is not set by the time we init the iommu
because, AFAICT, we do the latter in pci_iommu_init() and that's a
rootfs_initcall() which happens later then the CPU init stuff.

> I'll look into simplifying the checks.

Something like this maybe?

	if (rev >= 0x1205)
		return true;

	if (rev <= 0x11ff && rev >= 0x1126)
		return true;

	return false;

> > WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
> > #134: FILE: drivers/iommu/amd_iommu.c:866:
> > +static void build_completion_wait(struct iommu_cmd *cmd, volatile u64 *sem)
> > 
> 
> The semaphore area is written to by the device so the use of volatile is
> appropriate in this case.

Do you mean this is like the last exception case in that document above:

"
  - Pointers to data structures in coherent memory which might be modified
    by I/O devices can, sometimes, legitimately be volatile.  A ring buffer
    used by a network adapter, where that adapter changes pointers to
    indicate which descriptors have been processed, is an example of this
    type of situation."

?

If so, it did work fine until now, without the volatile. Why is it
needed now, all of a sudden?

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.