Re: [Xen-devel] [PATCH v2 3/3] x86/setup: remap Xen image up to PFN_DOWN(__pa(_end))

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.12.17 at 16:12, <daniel.kiper@xxxxxxxxxx> wrote:
> On Thu, Dec 07, 2017 at 05:02:02AM -0700, Jan Beulich wrote:
>> >>> On 04.12.17 at 11:24, <daniel.kiper@xxxxxxxxxx> wrote:
>> > Current limit, PFN_DOWN(xen_phys_start), introduced by commit b280442
>> > (x86: make Xen early boot code relocatable) is not reliable. Potentially
>> > its value may fall below PFN_DOWN(__pa(_end))
>>
>> Under what (perhaps just theoretical) conditions? It seems to imply
>> to me that we'd be moved Xen downwards if this was to happen, in
>> which case I'd suggest to simply skip the relocation instead (we
>> really only ever want to move Xen upwards).
> 
> Not always. If __pa(__image_base__) > xen_phys_start and even

I'm being increasingly confused: Isn't xen_phys_start identical to
__pa(__image_base__)?

> if xen_phys_start < __pa(_end) then we are still moving upwards.

And xen_phys_start always below __pa(_end)?

> That is why we should change the condition. And we have to reference
> to something constant not to the moving one.

I also don't understand what would be "the moving one" here:
xen_phys_start is being updated just once, before any of the
relocation code executes.

Jan


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