[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH] x86/HVM: expose VM assist hypercall

On 02.04.2020 21:49, Andrew Cooper wrote:
> On 02/04/2020 08:46, Jan Beulich wrote:
>> In preparation for the addition of VMASST_TYPE_runstate_update_flag
>> commit 72c538cca957 ("arm: add support for vm_assist hypercall") enabled
>> the hypercall for Arm. I consider it not logical that it then isn't also
>> exposed to x86 HVM guests (with the same single feature permitted to be
>> enabled as Arm has); Linux actually tries to use it afaict.
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> I'd declare this a bug in 2529c850ea4.  It was clearly intended as a
> common feature, and wasn't tested for HVM guests.
> However, ...
>> --- a/xen/arch/x86/hvm/hypercall.c
>> +++ b/xen/arch/x86/hvm/hypercall.c
>> @@ -78,6 +78,11 @@ static long hvm_grant_table_op(
>>  }
>>  #endif
>> +static long hvm_vm_assist(unsigned int cmd, unsigned int type)
>> +{
>> +    return vm_assist(current->domain, cmd, type, HVM_VM_ASSIST_VALID);
>> +}
>> +
>>  static long hvm_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
>>  {
>>      const struct vcpu *curr = current;
>> @@ -128,6 +133,7 @@ static const hypercall_table_t hvm_hyper
>>      HVM_CALL(grant_table_op),
>>  #endif
>> +    HVM_CALL(vm_assist),
> ... this means we've now got 3 stub functions making no-op ABI changes
> for the general vm_assist() function.

Not sure what you mean with "no-op" here. It's not like the
mask values would all be the same.

> Renaming it to do_vm_assist(), latch current->domain internally, and an
> arch_vm_assist_valid(d) helper can cover the final parameter.

I can certainly do this, but it very much seems to me to be a
request you'd call "scope creep". I was meaning to address the
issue at hand with a minimally invasive change. The bigger
variant you suggest is unlikely to cause backporting issues,
yes, but still ... Anyway, I'll do as you ask, to cut the
discussion short.




Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.