linux-kernel - Re: [RFC PATCH v3 04/20] x86: Handle reduction in physical address size with SME

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Date:   Tue, 15 Nov 2016 10:06:16 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     Joerg Roedel <joro@...tes.org>, <linux-arch@...r.kernel.org>,
        <linux-efi@...r.kernel.org>, <kvm@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <x86@...nel.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>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Larry Woodman <lwoodman@...hat.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>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v3 04/20] x86: Handle reduction in physical address
 size with SME

On 11/15/2016 9:33 AM, Borislav Petkov wrote:
> On Tue, Nov 15, 2016 at 08:40:05AM -0600, Tom Lendacky wrote:
>> The feature may be present and enabled even if it is not currently
>> active.  In other words, the SYS_CFG MSR bit could be set but we aren't
>> actually using encryption (sme_me_mask is 0).  As long as the SYS_CFG
>> MSR bit is set we need to take into account the physical reduction in
>> address space.
> 
> But later in the series I see sme_early_mem_enc() which tests exactly
> that mask.

Yes, but that doesn't relate to the physical address space reduction.

Once the SYS_CFG MSR bit for SME is set, even if the encryption bit is
never used, there is a physical reduction of the address space. So when
checking whether to adjust the physical address bits I can't rely on the
sme_me_mask, I have to look at the MSR.

But when I'm looking to decide whether to encrypt or decrypt something,
I use the sme_me_mask to decide if that is needed.  If the sme_me_mask
is not set then the encrypt/decrypt op shouldn't be performed.

I might not be grasping the point you're trying to make...

Thanks,
Tom

> 
> And in patch 12 you have:
> 
> +       /*
> +        * If memory encryption is active, the trampoline area will need to
> +        * be in un-encrypted memory in order to bring up other processors
> +        * successfully.
> +        */
> +       sme_early_mem_dec(__pa(base), size);
> +       sme_set_mem_unenc(base, size);
> 
> What's up?
> 
> IOW, it all sounds to me like you want to have an sme_active() helper
> and use it everywhere.
>