Re: [XEN PATCH v12 2/7] x86/pvh: Allow (un)map_pirq when dom0 is PVH

["Chen, Jiqian" <Jiqian.Chen@xxxxxxx>]

On 2024/7/30 21:09, Andrew Cooper wrote:
> On 08/07/2024 12:41 pm, Jiqian Chen wrote:
>> If run Xen with PVH dom0 and hvm domU, hvm will map a pirq for
>> a passthrough device by using gsi, see qemu code
>> xen_pt_realize->xc_physdev_map_pirq and libxl code
>> pci_add_dm_done->xc_physdev_map_pirq. Then xc_physdev_map_pirq
>> will call into Xen, but in hvm_physdev_op, PHYSDEVOP_map_pirq
>> is not allowed because currd is PVH dom0 and PVH has no
>> X86_EMU_USE_PIRQ flag, it will fail at has_pirq check.
>>
>> So, allow PHYSDEVOP_map_pirq when dom0 is PVH and also allow
>> PHYSDEVOP_unmap_pirq for the removal device path to unmap pirq.
>> And add a new check to prevent (un)map when the subject domain
>> doesn't have a notion of PIRQ.
>>
>> So that the interrupt of a passthrough device can be
>> successfully mapped to pirq for domU with a notion of PIRQ
>> when dom0 is PVH
>>
>> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
>> Signed-off-by: Huang Rui <ray.huang@xxxxxxx>
>> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
>> ---
>>  xen/arch/x86/hvm/hypercall.c |  6 ++++++
>>  xen/arch/x86/physdev.c       | 12 ++++++++++--
>>  2 files changed, 16 insertions(+), 2 deletions(-)
>>
>> diff --git a/xen/arch/x86/hvm/hypercall.c b/xen/arch/x86/hvm/hypercall.c
>> index 0fab670a4871..03ada3c880bd 100644
>> --- a/xen/arch/x86/hvm/hypercall.c
>> +++ b/xen/arch/x86/hvm/hypercall.c
>> @@ -71,8 +71,14 @@ long hvm_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) 
>> arg)
>>  
>>      switch ( cmd )
>>      {
>> +        /*
>> +        * Only being permitted for management of other domains.
>> +        * Further restrictions are enforced in do_physdev_op.
>> +        */
>>      case PHYSDEVOP_map_pirq:
>>      case PHYSDEVOP_unmap_pirq:
>> +        break;
>> +
>>      case PHYSDEVOP_eoi:
>>      case PHYSDEVOP_irq_status_query:
>>      case PHYSDEVOP_get_free_pirq:
>> diff --git a/xen/arch/x86/physdev.c b/xen/arch/x86/physdev.c
>> index d6dd622952a9..9f30a8c63a06 100644
>> --- a/xen/arch/x86/physdev.c
>> +++ b/xen/arch/x86/physdev.c
>> @@ -323,7 +323,11 @@ ret_t do_physdev_op(int cmd, 
>> XEN_GUEST_HANDLE_PARAM(void) arg)
>>          if ( !d )
>>              break;
>>  
>> -        ret = physdev_map_pirq(d, map.type, &map.index, &map.pirq, &msi);
>> +        /* Only mapping when the subject domain has a notion of PIRQ */
>> +        if ( !is_hvm_domain(d) || has_pirq(d) )
>> +            ret = physdev_map_pirq(d, map.type, &map.index, &map.pirq, 
>> &msi);
>> +        else
>> +            ret = -EOPNOTSUPP;
>>  
>>          rcu_unlock_domain(d);
>>  
>> @@ -346,7 +350,11 @@ ret_t do_physdev_op(int cmd, 
>> XEN_GUEST_HANDLE_PARAM(void) arg)
>>          if ( !d )
>>              break;
>>  
>> -        ret = physdev_unmap_pirq(d, unmap.pirq);
>> +        /* Only unmapping when the subject domain has a notion of PIRQ */
>> +        if ( !is_hvm_domain(d) || has_pirq(d) )
>> +            ret = physdev_unmap_pirq(d, unmap.pirq);
>> +        else
>> +            ret = -EOPNOTSUPP;
>>  
>>          rcu_unlock_domain(d);
>>  
> 
> Gitlab is displeased with your offering.
> 
> https://gitlab.com/xen-project/xen/-/pipelines/1393459622
> 
> This breaks both {adl,zen3p}-pci-hvm-x86-64-gcc-debug, and given the:
> 
> (XEN) [    8.150305] HVM restore d1: CPU 0
> libxl: error: libxl_pci.c:1491:pci_add_dm_done: Domain
> 1:xc_physdev_map_pirq irq=18 (error=-1): Not supported
> libxl: error: libxl_pci.c:1809:device_pci_add_done: Domain
> 1:libxl__device_pci_add failed for PCI device 0:3:0.0 (rc -3)
> libxl: error: libxl_create.c:1962:domcreate_attach_devices: Domain
> 1:unable to add pci devices
> libxl: error: libxl_xshelp.c:206:libxl__xs_read_mandatory: xenstore read
> failed: `/libxl/1/type': No such file or directory
> libxl: warning: libxl_dom.c:49:libxl__domain_type: unable to get domain
> type for domid=1, assuming HVM
> libxl: error: libxl_domain.c:1616:domain_destroy_domid_cb: Domain
> 1:xc_domain_destroy failed: No such process

Sorry to forget to validate the scenario of "hvm_pirq=0" for HVM guest since 
V10->V11(remove the self-check "d == currd").

V10 version:
+        /* Prevent self-map when currd has no X86_EMU_USE_PIRQ flag */
+        if ( is_hvm_domain(d) && !has_pirq(d) && d == currd )
+        {
+            rcu_unlock_domain(d);
+            return -EOPNOTSUPP;
+        }

V11 version:
+        /* Prevent mapping when the subject domain has no X86_EMU_USE_PIRQ */
+        if ( is_hvm_domain(d) && !has_pirq(d) )
+        {
+            rcu_unlock_domain(d);
+            return -EOPNOTSUPP;
+        }

V10 is fine for when hvm_pirq is enable or disable. 
This issue is from V11, the cause is that when pass "hvm_pirq=0" to HVM guest, 
then has_pirq() is false, but it still uses the pirq to route the interrupt of 
passthrough devices.
So, it still does xc_physdev_(un)map_pirq, then fails at the has_pirq() check.

Hi Jan,
Should I need to change to V10 to only prevent the self-mapping when the 
subject domain has no PIRQ?
So that it can allow PHYSDEVOP_map_pirq for foreign mapping, no matter the dom0 
or the domU has PIRQ or not?

> 
> I'd say that we're hitting the newly introduced -EOPNOTSUPP path.
> 
> In the test scenario, dom0 is PV, and it's an HVM domU which is breaking.
> 
> The sibling *-pci-pv-* tests (a PV domU) are working fine.
> 
> Either way, I'm going to revert this for now because clearly the "the
> subject domain has a notion of PIRQ" hasn't been reasoned about
> correctly, and it's important to keep Gitlab CI green across the board.
> 
> ~Andrew

-- 
Best regards,
Jiqian Chen.