Re: [Xen-devel] [PATCH v6 7/9] xen/mem_access: Use __get_gfn_type_access in set_mem_access

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.01.2020 14:53, Tamas K Lengyel wrote:
> On Wed, Jan 29, 2020 at 6:10 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>
>> On 27.01.2020 19:06, Tamas K Lengyel wrote:
>>> Use __get_gfn_type_access instead of p2m->get_entry to trigger page-forking
>>> when the mem_access permission is being set on a page that has not yet been
>>> copied over from the parent.
>>
>> You talking of page-forking here, don't you mean ...
>>
>>> --- a/xen/arch/x86/mm/mem_access.c
>>> +++ b/xen/arch/x86/mm/mem_access.c
>>> @@ -303,11 +303,10 @@ static int set_mem_access(struct domain *d, struct 
>>> p2m_domain *p2m,
>>>      ASSERT(!ap2m);
>>>  #endif
>>>      {
>>> -        mfn_t mfn;
>>>          p2m_access_t _a;
>>>          p2m_type_t t;
>>> -
>>> -        mfn = p2m->get_entry(p2m, gfn, &t, &_a, 0, NULL, NULL);
>>> +        mfn_t mfn = __get_gfn_type_access(p2m, gfn_x(gfn), &t, &_a,
>>> +                                          P2M_ALLOC, NULL, false);
>>
>> ... P2M_UNSHARE here?
> 
> No, P2M_UNSHARE is only required if you are doing a memory write.
> Setting memory access permissions is not a memory write, so it's
> sufficient to just allocate the p2m entry. P2M_ALLOCATE also
> encompasses forking the entry if there is a parent VM.

Ah, I see. And hence
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

>> Also shouldn't you have Cc-ed Petre and Alexandru on this patch
>> (for their R: entries) and at least George (perhaps also Andrew
>> and me) to get an ack, seeing that you're the only maintainer
>> of the file?
> 
> I've ran ./add_maintainers.pl on the patches, not sure why noone else got 
> CC-d.

It not picking up R: entries would seem like a bug to me. It not
knowing of nesting of maintainership is entirely expected (or
else it would also need to know that it's - in this case - you
who is invoking it).

Jan

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