Re: [Xen-devel] [PATCH] x86: correct assertion in destroy_perdomain_mapping()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 20/04/18 16:27, Jan Beulich wrote:
>>>> On 20.04.18 at 17:21, <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 20/04/18 16:03, Jan Beulich wrote:
>>> hvm_domain_initialise() may call this with nr being zero, which triggers
>>> the "does not cross L3 boundary" check.
>>>
>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> Is this the correct fix?
>>
>> Its unclear what the call to create_perdomain_mapping() is doing, but it
>> is the sole caller which passes 0.
>>
>> I presume it is to allocate d->arch.perdomain_l3_pg but
>> destroy_perdomain_mapping() doesn't free this page, so I've got no idea
>> what the destroy call is trying to achieve.
> Callers of this pair of functions should not be concerned about their
> inner workings: If the create call succeeded, the destroy function should
> be called for cleanup, even if that's _currently_ a no-op.

Right, but its still not clear that passing 0 (even to create) is a
legitimate thing to do.

~Andrew

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