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Re: [Xen-devel] [PATCH 11/14] xen/x86: mm: Re-implement set_gpfn_from_mfn() as a static inline function


On 10/05/2019 14:48, Jan Beulich wrote:
On 10.05.19 at 15:41, <julien.grall@xxxxxxx> wrote:
On 10/05/2019 14:35, Jan Beulich wrote:
On 10.05.19 at 15:27, <julien.grall@xxxxxxx> wrote:
On 10/05/2019 13:43, Jan Beulich wrote:
On 07.05.19 at 17:14, <julien.grall@xxxxxxx> wrote:
+static inline void set_gpfn_from_mfn(unsigned long mfn, unsigned long pfn)
+    struct domain *d = page_get_owner(mfn_to_page(_mfn(mfn)));
+    unsigned long entry = (d && (d == dom_cow)) ? SHARED_M2P_ENTRY : pfn;

The && here looks, ehm, funny, but I guess it's needed for early boot?

I have no idea, this is x86 not Arm...

But that's perhaps a separate thing to clean up. However, looking at
this - why is Arm setting up dom_cow in the first place?

Common code is using dom_cow, so I don't think we want it to be NULL on Arm to
avoid weird issues.

I didn't mean it to remain NULL. Common code doesn't dereference it
(and isn't supposed to), so I'd consider initializing it to some known
faulting non-NULL address, if there is such on Arm.

Patches are welcomed ;).

So is there such an address on Arm?

0 - 2MB is unmapped so far. I don't know whether this will still be the case (at least for the range 4KB - 2MB) with the rework I am attempting.


Julien Grall

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