linux-kernel - Re: [PATCH v7 08/36] x86/mm: Add support to enable SME in early boot processing

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Date:   Wed, 21 Jun 2017 13:30:19 -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 08/36] x86/mm: Add support to enable SME in early boot
 processing

On 6/21/2017 10:38 AM, Thomas Gleixner wrote:
> On Wed, 21 Jun 2017, Tom Lendacky wrote:
>> On 6/21/2017 2:16 AM, Thomas Gleixner wrote:
>>> Why is this an unconditional function? Isn't the mask simply 0 when the MEM
>>> ENCRYPT support is disabled?
>>
>> I made it unconditional because of the call from head_64.S. I can't make
>> use of the C level static inline function and since the mask is not a
>> variable if CONFIG_AMD_MEM_ENCRYPT is not configured (#defined to 0) I
>> can't reference the variable directly.
>>
>> I could create a #define in head_64.S that changes this to load rax with
>> the variable if CONFIG_AMD_MEM_ENCRYPT is configured or a zero if it's
>> not or add a #ifdef at that point in the code directly. Thoughts on
>> that?
> 
> See below.
> 
>>> That does not make any sense. Neither the call to sme_encrypt_kernel() nor
>>> the following call to sme_get_me_mask().
>>>
>>> __startup_64() is already C code, so why can't you simply call that from
>>> __startup_64() in C and return the mask from there?
>>
>> I was trying to keep it explicit as to what was happening, but I can
>> move those calls into __startup_64().
> 
> That's much preferred. And the return value wants to be documented in both
> C and ASM code.

Will do.

> 
>> I'll still need the call to sme_get_me_mask() in the secondary_startup_64
>> path, though (depending on your thoughts to the above response).
> 
>          call verify_cpu
> 
>          movq    $(init_top_pgt - __START_KERNEL_map), %rax
> 
> So if you make that:
> 
> 	/*
> 	 * Sanitize CPU configuration and retrieve the modifier
> 	 * for the initial pgdir entry which will be programmed
> 	 * into CR3. Depends on enabled SME encryption, normally 0.
> 	 */
> 	call __startup_secondary_64
> 
>          addq    $(init_top_pgt - __START_KERNEL_map), %rax
> 
> You can hide that stuff in C-code nicely without adding any cruft to the
> ASM code.
> 

Moving the call to verify_cpu into the C-code might be quite a bit of
change.  Currently, the verify_cpu code is included code and not a
global function.  I can still do the __startup_secondary_64() function
and then look to incorporate verify_cpu into both __startup_64() and
__startup_secondary_64() as a post-patch to this series. At least the
secondary path will have a base C routine to which modifications can
be made in the future if needed.  How does that sound?

Thanks,
Tom

> Thanks,
> 
> 	tglx
>