Re: [PATCH v2 2/3] xen/arm: make has_vpci depend on CONFIG_HAS_VPCI

[Stewart Hildebrand <stewart.hildebrand@xxxxxxx>]

On 7/7/23 04:55, Julien Grall wrote:
> Hi,
> 
> On 07/07/2023 02:47, Stewart Hildebrand wrote:
>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>>
>> VPCI is disabled on ARM. Make it depend on CONFIG_HAS_VPCI to test the PCI
>> passthrough support. Also make it depend on is_hardware_domain for now. The
>> is_hardware_domain check should be removed when vPCI is upstreamed.
>>
>> While here, remove the comment on the preceding line.
>>
>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>> Signed-off-by: Rahul Singh <rahul.singh@xxxxxxx>
>> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
>> ---
>> There are two downstreams [1] [2] that have independently made a version this
>> change, each with different Signed-off-by's. I simply picked one at random 
>> for
>> the Author: field, and added both Signed-off-by lines. Please let me know if
>> there are any objections.
>>
>> v1->v2:
>> * add is_hardware_domain check. This will need to be removed after the vPCI
>>    series [3] is merged.
>>
>> downstream->v1:
>> * change to IS_ENABLED(CONFIG_HAS_VPCI) instead of hardcoded to true
>> * remove the comment on the preceding line
>>
>> [1] 
>> https://gitlab.com/xen-project/people/bmarquis/xen-arm-poc/-/commit/27be1729ce8128dbe37275ce7946b2fbd2e5a382
>> [2] 
>> https://github.com/xen-troops/xen/commit/bf12185e6fb2e31db0d8e6ea9ccd8a02abadec17
>> [3] 
>> https://lists.xenproject.org/archives/html/xen-devel/2023-06/msg00863.html
>> ---
>>   xen/arch/arm/include/asm/domain.h | 3 +--
>>   1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/xen/arch/arm/include/asm/domain.h 
>> b/xen/arch/arm/include/asm/domain.h
>> index 99e798ffff68..1a13965a26b8 100644
>> --- a/xen/arch/arm/include/asm/domain.h
>> +++ b/xen/arch/arm/include/asm/domain.h
>> @@ -298,8 +298,7 @@ static inline void arch_vcpu_block(struct vcpu *v) {}
>>
>>   #define arch_vm_assist_valid_mask(d) (1UL << 
>> VMASST_TYPE_runstate_update_flag)
>>
>> -/* vPCI is not available on Arm */
>> -#define has_vpci(d)    ({ (void)(d); false; })
>> +#define has_vpci(d) ({ IS_ENABLED(CONFIG_HAS_VPCI) && 
>> is_hardware_domain(d); })
> 
> So in v1, I asked whether we should use is_hardware_domain() or
> d->arch.pci. I see you went with the former, but wouldn't this mean that
> the vPCI is always enabled for dom0 when CONFIG_HAS_VPCI=y?

Yes...

> Shouldn't this instead be conditional to pci_passthrough_enabled?

That could be a possibility, however, in v5 of the PCI ARM SMMU series [4], we 
propose removing the pci_passthrough_enabled flag (as a way to use PCI devices 
in dom0 without pci-passthrough=yes). If pci_passthrough_enabled is gone, the 
conditions under which vpci should be enabled for dom0 aren't entirely clear to 
me (other than CONFIG_HAS_VPCI=y).

[4] https://lists.xenproject.org/archives/html/xen-devel/2023-10/msg00210.html

> So you could return d->arch.pci in has_vcpi(). The field would be set by
> domain_create() based on the flags passed by the caller. I would
> properly plumb to xen_domctl_createdomain and has a check in
> arch_sanitise_domain_config() to confirm the flag can be set.

I'll plumb this for v3 of this series.

> 
> Cheers,
> 
> -- 
> Julien Grall