linux-kernel - Re: [RFC v1 23/26] x86/tdx: Make pages shared in ioremap()

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Date:   Tue, 6 Apr 2021 09:14:53 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v1 23/26] x86/tdx: Make pages shared in ioremap()

On 4/6/21 9:00 AM, Kirill A. Shutemov wrote:
>>> --- a/arch/x86/mm/ioremap.c
>>> +++ b/arch/x86/mm/ioremap.c
>>> @@ -87,12 +87,12 @@ static unsigned int __ioremap_check_ram(struct resource *res)
>>>  }
>>>  
>>>  /*
>>> - * In a SEV guest, NONE and RESERVED should not be mapped encrypted because
>>> - * there the whole memory is already encrypted.
>>> + * In a SEV or TDX guest, NONE and RESERVED should not be mapped encrypted (or
>>> + * private in TDX case) because there the whole memory is already encrypted.
>>>   */
>> But doesn't this mean that we can't ioremap() normal memory?
> It's not allowed anyway: see (io_desc.flags & IORES_MAP_SYSTEM_RAM) in the
> __ioremap_caller().
> 
>> I was somehow expecting that we would need to do this for some
>> host<->guest communication pages.
> It goes though DMA API, not ioremap().

Ahh, got it.  Thanks for the clarification.

It would help to make mention of that stuff in the changelog to make it
more obvious going forward.