Re: [Xen-devel] [PATCH v2 1/2] arm/mem_access: adjust check_and_get_page to not rely on current

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 12/12/16 23:47, Tamas K Lengyel wrote:
>
>> It works on x86 because, IIRC, you do a software page table walking.
>> Although, I don't think you have particular write/read access checking on
>> x86.
> I don't recall there being any software page walking being involved on
> x86. Why would that be needed? On x86 we get the guest physical
> address recorded by the CPU automatically. AFAIK in case the pagetable
> was unaccessible for the translation of a VA, we would get an event
> with the pagetable's PA and the type of event that generated it (ie.
> reading during translation).

x86 provides no mechanism to have hardware translate an address in a
separate context.  Therefore, all translations which are necessary need
to be done in hardware.

Newer versions of VT-x/SVM may provide additional information on a
vmexit, which include a guest physical address relevant to the the
reason for the vmexit.

Xen will attempt to proactively use this information to avoid a software
pagewalk, but can always fall back to the software method if needs be.


I presume ARM has always relied on hardware support for translation, and
has no software translation support?  I presume therefore that
translations only work when in current context?

~Andrew

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel