linux-kernel - Re: [RFC v2 26/32] x86/mm: Move force_dma

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Date:   Mon, 17 May 2021 16:11:31 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Dave Hansen <dave.hansen@...el.com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Raj Ashok <ashok.raj@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC v2 26/32] x86/mm: Move force_dma_unencrypted() to common
 code


On 5/17/2021 3:32 PM, Kuppuswamy, Sathyanarayanan wrote:
>
>
> On 5/17/21 11:37 AM, Sean Christopherson wrote:
>>> Just remember, a "common framework" doesn't mean that it can't be 
>>> backed
>>> by extremely arch-specific mechanisms.
>>>
>>> For instance, there's a lot of pkey-specific code in mm/mprotect.c.  It
>>> still gets optimized away on x86 with all the goodness of X86_FEATUREs.
>> Ya, exactly.  Ideally, generic code shouldn't have to differentiate 
>> between SEV,
>> SEV-ES, SEV-SNP, TDX, etc..., a vanilla "bool 
>> is_protected_guest(void)" should
>> suffice.  Under the hood, x86's implementation for 
>> is_protected_guest() can be
>> boot_cpu_has() checks (if we want).
>
> What about the use case of protected_guest_has(flag)? Do you want to 
> call it with
> with X86_FEATURE_* flags outside arch/x86 code ?


I don't think we need any flags in the generic code. Just a simple bool 
is enough.


-Andi