Re: [Xen-devel] [PATCH v4 05/18] x86/mem_sharing: don't try to unshare twice during page fault

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.01.2020 16:59, Tamas K Lengyel wrote:
> On Thu, Jan 16, 2020 at 7:55 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>
>> On 08.01.2020 18:14, Tamas K Lengyel wrote:
>>> @@ -1702,11 +1703,14 @@ int hvm_hap_nested_page_fault(paddr_t gpa, unsigned 
>>> long gla,
>>>      struct domain *currd = curr->domain;
>>>      struct p2m_domain *p2m, *hostp2m;
>>>      int rc, fall_through = 0, paged = 0;
>>> -    int sharing_enomem = 0;
>>>      vm_event_request_t *req_ptr = NULL;
>>>      bool sync = false;
>>>      unsigned int page_order;
>>>
>>> +#ifdef CONFIG_MEM_SHARING
>>> +    bool sharing_enomem = false;
>>> +#endif
>>
>> To reduce #ifdef-ary, could you leave this alone (or convert to
>> bool in place, without #ifdef) and ...
>>
>>> @@ -1955,19 +1961,21 @@ int hvm_hap_nested_page_fault(paddr_t gpa, unsigned 
>>> long gla,
>>>       */
>>>      if ( paged )
>>>          p2m_mem_paging_populate(currd, gfn);
>>> +
>>> +#ifdef CONFIG_MEM_SHARING
>>>      if ( sharing_enomem )
>>>      {
>>> -        int rv;
>>> -
>>> -        if ( (rv = mem_sharing_notify_enomem(currd, gfn, true)) < 0 )
>>> +        if ( !vm_event_check_ring(currd->vm_event_share) )
>>>          {
>>> -            gdprintk(XENLOG_ERR, "Domain %hu attempt to unshare "
>>> -                     "gfn %lx, ENOMEM and no helper (rc %d)\n",
>>> -                     currd->domain_id, gfn, rv);
>>> +            gprintk(XENLOG_ERR, "Domain %pd attempt to unshare "
>>> +                    "gfn %lx, ENOMEM and no helper\n",
>>> +                    currd, gfn);
>>>              /* Crash the domain */
>>>              rc = 0;
>>>          }
>>>      }
>>> +#endif
>>
>> ... move the #ifdef inside the braces here? With this
>> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> SGTM, I assume you are counting on the compiler to just get rid of the
> variable when it sees its never used?

Yes (and for un-optimized code it doesn't matter).

Jan

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