Re: [Xen-devel] [PATCH V5 08/12] xen/vm_event: Check for VM_EVENT_FLAG_DUMMY only in Debug builds

[Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>]

On Fri, Feb 13, 2015 at 9:14 PM, Andrew Cooper
<andrew.cooper3@xxxxxxxxxx> wrote:
> On 13/02/15 16:33, Tamas K Lengyel wrote:
>> The flag is only used for debugging purposes, thus it should be only checked
>> for in debug builds of Xen.
>>
>> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
>
> What is the purpose of the dummy flag?  I would have thought it would be
> more dangerous to accidentally process a dummy response in a non-debug Xen.
>
> ~Andrew

I honestly have no idea what was the real use-case for it. It is a way
to signal to Xen to just remove the reponse from the ring without
doing anything else with it so I figured it might be handy when
debugging a toolstack.

Tamas

>
>> ---
>>  xen/arch/x86/mm/mem_sharing.c | 2 ++
>>  xen/arch/x86/mm/p2m.c         | 2 ++
>>  xen/common/mem_access.c       | 2 ++
>>  3 files changed, 6 insertions(+)
>>
>> diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
>> index 4e5477a..0459544 100644
>> --- a/xen/arch/x86/mm/mem_sharing.c
>> +++ b/xen/arch/x86/mm/mem_sharing.c
>> @@ -606,8 +606,10 @@ int mem_sharing_sharing_resume(struct domain *d)
>>              continue;
>>          }
>>
>> +#ifndef NDEBUG
>>          if ( rsp.flags & VM_EVENT_FLAG_DUMMY )
>>              continue;
>> +#endif
>>
>>          /* Validate the vcpu_id in the response. */
>>          if ( (rsp.vcpu_id >= d->max_vcpus) || !d->vcpu[rsp.vcpu_id] )
>> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
>> index 5ce852e..68d57d7 100644
>> --- a/xen/arch/x86/mm/p2m.c
>> +++ b/xen/arch/x86/mm/p2m.c
>> @@ -1312,8 +1312,10 @@ void p2m_mem_paging_resume(struct domain *d)
>>              continue;
>>          }
>>
>> +#ifndef NDEBUG
>>          if ( rsp.flags & VM_EVENT_FLAG_DUMMY )
>>              continue;
>> +#endif
>>
>>          /* Validate the vcpu_id in the response. */
>>          if ( (rsp.vcpu_id >= d->max_vcpus) || !d->vcpu[rsp.vcpu_id] )
>> diff --git a/xen/common/mem_access.c b/xen/common/mem_access.c
>> index a6d82d1..63f2b52 100644
>> --- a/xen/common/mem_access.c
>> +++ b/xen/common/mem_access.c
>> @@ -44,8 +44,10 @@ void mem_access_resume(struct domain *d)
>>              continue;
>>          }
>>
>> +#ifndef NDEBUG
>>          if ( rsp.flags & VM_EVENT_FLAG_DUMMY )
>>              continue;
>> +#endif
>>
>>          /* Validate the vcpu_id in the response. */
>>          if ( (rsp.vcpu_id >= d->max_vcpus) || !d->vcpu[rsp.vcpu_id] )
>

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