Re: [PATCH v4 05/11] vpci/header: implement guest BAR register handlers

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>]

On 19.11.21 14:49, Jan Beulich wrote:
> On 19.11.2021 13:46, Oleksandr Andrushchenko wrote:
>> On 19.11.21 14:37, Jan Beulich wrote:
>>> On 19.11.2021 13:10, Oleksandr Andrushchenko wrote:
>>>> On 19.11.21 13:58, Jan Beulich wrote:
>>>>> On 05.11.2021 07:56, Oleksandr Andrushchenko wrote:
>>>>>> --- a/xen/drivers/vpci/header.c
>>>>>> +++ b/xen/drivers/vpci/header.c
>>>>>> @@ -408,6 +408,48 @@ static void bar_write(const struct pci_dev *pdev, 
>>>>>> unsigned int reg,
>>>>>>         pci_conf_write32(pdev->sbdf, reg, val);
>>>>>>     }
>>>>>>     
>>>>>> +static void guest_bar_write(const struct pci_dev *pdev, unsigned int 
>>>>>> reg,
>>>>>> +                            uint32_t val, void *data)
>>>>>> +{
>>>>>> +    struct vpci_bar *bar = data;
>>>>>> +    bool hi = false;
>>>>>> +
>>>>>> +    if ( bar->type == VPCI_BAR_MEM64_HI )
>>>>>> +    {
>>>>>> +        ASSERT(reg > PCI_BASE_ADDRESS_0);
>>>>>> +        bar--;
>>>>>> +        hi = true;
>>>>>> +    }
>>>>>> +    else
>>>>>> +    {
>>>>>> +        val &= PCI_BASE_ADDRESS_MEM_MASK;
>>>>>> +        val |= bar->type == VPCI_BAR_MEM32 ? 
>>>>>> PCI_BASE_ADDRESS_MEM_TYPE_32
>>>>>> +                                           : 
>>>>>> PCI_BASE_ADDRESS_MEM_TYPE_64;
>>>>>> +        val |= bar->prefetchable ? PCI_BASE_ADDRESS_MEM_PREFETCH : 0;
>>>>>> +    }
>>>>>> +
>>>>>> +    bar->guest_addr &= ~(0xffffffffull << (hi ? 32 : 0));
>>>>>> +    bar->guest_addr |= (uint64_t)val << (hi ? 32 : 0);
>>>>>> +
>>>>>> +    bar->guest_addr &= ~(bar->size - 1) | ~PCI_BASE_ADDRESS_MEM_MASK;
>>>>>> +}
>>>>>> +
>>>>>> +static uint32_t guest_bar_read(const struct pci_dev *pdev, unsigned int 
>>>>>> reg,
>>>>>> +                               void *data)
>>>>>> +{
>>>>>> +    const struct vpci_bar *bar = data;
>>>>>> +    bool hi = false;
>>>>>> +
>>>>>> +    if ( bar->type == VPCI_BAR_MEM64_HI )
>>>>>> +    {
>>>>>> +        ASSERT(reg > PCI_BASE_ADDRESS_0);
>>>>>> +        bar--;
>>>>>> +        hi = true;
>>>>>> +    }
>>>>>> +
>>>>>> +    return bar->guest_addr >> (hi ? 32 : 0);
>>>>> I'm afraid "guest_addr" then isn't the best name; maybe "guest_val"?
>>>>> This would make more obvious that there is a meaningful difference
>>>>> from "addr" besides the guest vs host aspect.
>>>> I am not sure I can agree here:
>>>> bar->addr and bar->guest_addr make it clear what are these while
>>>> bar->addr and bar->guest_val would make someone go look for
>>>> additional information about what that val is for.
>>> Feel free to replace "val" with something more suitable. "guest_bar"
>>> maybe? The value definitely is not an address, so "addr" seems
>>> inappropriate / misleading to me.
>> This is a guest's view on the BAR's address. So to me it is still guest_addr
> It's a guest's view on the BAR, not just the address. Or else you couldn't
> simply return the value here without folding in the correct low bits.
I agree with this this respect as it is indeed address + lower bits.
How about guest_bar_val then? So it reflects its nature, e.g. the value
of the BAR as seen by the guest.
>
> Jan
>
Thank you,
Oleksandr