linux-kernel - Re: [PATCH] x86/mm: Rewrite sme_populate

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Message-ID: <d9701b1c-1abf-5fc1-80b0-47ab4e517681@amd.com>
Date:   Mon, 4 Dec 2017 10:00:26 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Borislav Petkov <bp@...e.de>,
        Brijesh Singh <brijesh.singh@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/mm: Rewrite sme_populate_pgd() in a more sensible way

On 12/4/2017 8:57 AM, Kirill A. Shutemov wrote:
> On Mon, Dec 04, 2017 at 08:19:11AM -0600, Tom Lendacky wrote:
>> On 12/4/2017 5:23 AM, Kirill A. Shutemov wrote:
>>> sme_populate_pgd() open-codes a lot of things that are not needed to be
>>> open-coded.
>>>
>>> Let's rewrite it in a more stream-lined way.
>>>
>>> This would also buy us boot-time switching between support between
>>> paging modes, when rest of the pieces will be upstream.
>>
>> Hi Kirill,
>>
>> Unfortunately, some of these can't be changed.  The use of p4d_offset(),
>> pud_offset(), etc., use non-identity mapped virtual addresses which cause
>> failures at this point of the boot process.
> 
> Wat? Virtual address is virtual address. p?d_offset() doesn't care about
> what mapping you're using.

Yes it does.  For example, pmd_offset() issues a pud_page_addr() call,
which does a __va() returning a non-identity mapped address (0xffff88...). 
  Only identity mapped virtual addresses have been setup at this point, so
the use of that virtual address panics the kernel.

Thanks,
Tom

> 
>> Also, calls such as __p4d(), __pud(), etc., are part of the paravirt
>> support and can't be used yet, either.
> 
> Yeah, I missed this. native_make_p?d() has to be used instead.
> 
>> I can take a closer look at some of the others (p*d_none() and
>> p*d_large()) which make use of the native_ macros, but my worry would be
>> that these get changed in the future to the non-native calls and then
>> boot failures occur.
> 
> If you want to avoid paravirt altogher for whole compilation unit, one
> more option would be to put #undef CONFIG_PARAVIRT before all includes.
> That's hack, but it works. We already use this in arch/x86/boot/compressed
> code.
>