linux-kernel - Re: [PATCH v7 07/36] x86/mm: Don't use phys_to

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Date:   Wed, 21 Jun 2017 08:52:53 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
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, xen-devel@...ts.xen.org,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Brijesh Singh <brijesh.singh@....com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Alexander Potapenko <glider@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Joerg Roedel <joro@...tes.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dave Young <dyoung@...hat.com>, Rik van Riel <riel@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Juergen Gross <jgross@...e.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v7 07/36] x86/mm: Don't use phys_to_virt in ioremap() if
 SME is active

On 6/20/2017 3:55 PM, Thomas Gleixner wrote:
> On Fri, 16 Jun 2017, Tom Lendacky wrote:
> 
>> Currently there is a check if the address being mapped is in the ISA
>> range (is_ISA_range()), and if it is then phys_to_virt() is used to
>> perform the mapping.  When SME is active, however, this will result
>> in the mapping having the encryption bit set when it is expected that
>> an ioremap() should not have the encryption bit set. So only use the
>> phys_to_virt() function if SME is not active
> 
> This does not make sense to me. What the heck has phys_to_virt() to do with
> the encryption bit. Especially why would the encryption bit be set on that
> mapping in the first place?

The default is that all entries that get added to the pagetables have
the encryption bit set unless specifically overridden.  Any __va() or
phys_to_virt() calls will result in a pagetable mapping that has the
encryption bit set.  For ioremap, the PAGE_KERNEL_IO protection is used
which will not/does not have the encryption bit set.

> 
> I'm probably missing something, but this want's some coherent explanation
> understandable by mere mortals both in the changelog and the code comment.

I'll add some additional info to the changelog and code.

Thanks,
Tom

> 
> Thanks,
> 
> 	tglx
>