On 27.07.2022 21:39, Oleksandr wrote:
> On 27.07.22 20:54, Oleksandr wrote:
>> On 26.07.22 18:16, Jan Beulich wrote:
>>> On 19.07.2022 19:42, Oleksandr Tyshchenko wrote:
>>>> --- a/xen/arch/arm/vpci.c
>>>> +++ b/xen/arch/arm/vpci.c
>>>> @@ -41,6 +41,16 @@ static int vpci_mmio_read(struct vcpu *v,
>>>> mmio_info_t *info,
>>>> /* data is needed to prevent a pointer cast on 32bit */
>>>> unsigned long data;
>>>> + /*
>>>> + * For the passed through devices we need to map their virtual
>>>> SBDF
>>>> + * to the physical PCI device being passed through.
>>>> + */
>>>> + if ( !bridge && !vpci_translate_virtual_device(v->domain, &sbdf) )
>>>> + {
>>>> + *r = ~0ul;
>>>> + return 1;
>>>> + }
>>> I'm probably simply lacking specific Arm-side knowledge, but it strikes
>>> me as odd that the need for translation would be dependent upon
>>> "bridge".
>>
>>
>> I am afraid I cannot answer immediately.
>>
>> I will analyze that question and provide an answer later on.
>
>
> Well, most likely that "valid" bridge pointer here is just used as an
> indicator of hwdom currently, so no need to perform virt->phys
> translation for sbdf.
>
> You can see that domain_vpci_init() passes a valid value for hwdom and
> NULL for other domains when setting up vpci_mmio* callbacks.
Oh, I see.
> Alternatively, I guess we could use "!is_hardware_domain(v->domain)"
> instead of "!bridge" in the first part of that check. Shall I?
Maybe simply add a comment? Surely checking "bridge" is cheaper than
using is_hardware_domain(), so I can see the benefit. But the larger
arm/vpci.c grows, the less obvious the connection will be without a
comment. (Instead of a comment, an alternative may be a suitable
assertion, which then documents the connection at the same time, e.g.
ASSERT(!bridge == !is_hardware_domain(v->domain)). But that won't be
possible in e.g. vpci_sbdf_from_gpa(), where apparently a similar
assumption is being made.)
Jan
