linux-kernel - Re: [PATCH v2 1/1] KVM: arm64: Allow cacheable stage 2 mapping using VMA flags

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Message-ID: <23fa05f8-ea30-4261-91d8-b34fc678c4de@redhat.com>
Date: Fri, 17 Jan 2025 17:58:29 +0100
From: David Hildenbrand <david@...hat.com>
To: Jason Gunthorpe <jgg@...dia.com>,
 Catalin Marinas <catalin.marinas@....com>
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Subject: Re: [PATCH v2 1/1] KVM: arm64: Allow cacheable stage 2 mapping using
 VMA flags


>> I don't see how VM_PFNMAP alone can tell us anything about the
>> access properties supported by a device address range. Either way,
>> it's the driver setting vm_page_prot or some VM_* flag. KVM has no
>> clue, it's just a memory slot.
> 
> I think David's point about VM_PFNMAP was to avoid some of the
> pfn_valid() logic. If we get VM_PFNMAP we just assume it is non-struct
> page and follow the VMA's pgprot.

Exactly what I meant.

If we only expect DEVICE stuff in VM_PFNMAP, then we can limit all the 
weirdness (and figuring out what todo using pgprot etc) to exactly that.

VM_IO without VM_PFNMAP might be interesting; not sure if we even want 
to support that here.

-- 
Cheers,

David / dhildenb