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]

Date:   Thu, 15 Jun 2017 17:33:22 +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 Thu, Jun 15, 2017 at 09:59:45AM -0500, Tom Lendacky wrote:
> Actually the detection routine, amd_iommu_detect(), is part of the
> IOMMU_INIT_FINISH macro support which is called early through mm_init()
> from start_kernel() and that routine is called before init_amd().

Ah, we do that there too:

	for (p = __iommu_table; p < __iommu_table_end; p++) {

Can't say that that code with the special section and whatnot is
obvious. :-\

Oh, well, early_init_amd() then. That is called in
start_kernel->setup_arch->early_cpu_init and thus before mm_init().

> > If so, it did work fine until now, without the volatile. Why is it
> > needed now, all of a sudden?
> 
> If you run checkpatch against the whole amd_iommu.c file you'll see that

I'm, of course, not talking about the signature change: I'm *actually*
questioning the need to make this argument volatile, all of a sudden.

If there's a need, please explain why. It worked fine until now. If it
didn't, we would've seen it.

If it is a bug, then it needs a proper explanation, a *separate* patch
and so on. But not like now, a drive-by change in an IOMMU enablement
patch.

If it is wrong, then wait_on_sem() needs to be fixed too. AFAICT,
wait_on_sem() gets called in both cases with interrupts disabled, while
holding a lock so I'd like to pls know why, even in that case, does this
variable need to be volatile.

-- 
Regards/Gruss,
    Boris.

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