Re: [PATCH v8 2/5] xen/arm: Enable the existing x86 virtual PCI support for ARM

[Jan Beulich <jbeulich@xxxxxxxx>]

On 18.10.2021 16:07, Oleksandr Andrushchenko wrote:
> On 18.10.21 13:29, Jan Beulich wrote:
>> On 18.10.2021 12:11, Bertrand Marquis wrote:
>>>> On 18 Oct 2021, at 08:47, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>>> On 15.10.2021 18:51, Bertrand Marquis wrote:
>>>>> --- /dev/null
>>>>> +++ b/xen/arch/arm/vpci.c
>>>>> @@ -0,0 +1,77 @@
>>>>> +/*
>>>>> + * xen/arch/arm/vpci.c
>>>>> + *
>>>>> + * This program is free software; you can redistribute it and/or modify
>>>>> + * it under the terms of the GNU General Public License as published by
>>>>> + * the Free Software Foundation; either version 2 of the License, or
>>>>> + * (at your option) any later version.
>>>>> + *
>>>>> + * This program is distributed in the hope that it will be useful,
>>>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>>>> + * GNU General Public License for more details.
>>>>> + */
>>>>> +#include <xen/sched.h>
>>>>> +#include <xen/vpci.h>
>>>>> +
>>>>> +#include <asm/mmio.h>
>>>>> +
>>>>> +static int vpci_mmio_read(struct vcpu *v, mmio_info_t *info,
>>>>> +                          register_t *r, void *p)
>>>>> +{
>>>>> +    pci_sbdf_t sbdf;
>>>>> +    /* data is needed to prevent a pointer cast on 32bit */
>>>>> +    unsigned long data;
>>>>> +
>>>>> +    /* We ignore segment part and always handle segment 0 */
>>>>> +    sbdf.sbdf = VPCI_ECAM_BDF(info->gpa);
>>>>> +
>>>>> +    if ( vpci_ecam_read(sbdf, ECAM_REG_OFFSET(info->gpa),
>>>>> +                        1U << info->dabt.size, &data) )
>>>>> +    {
>>>> Here it is quite clear that the SBDF you pass into vpci_ecam_read() is
>>>> the virtual one. The function then calls vpci_read(), which in turn
>>>> will call vpci_read_hw() in a number of situations (first and foremost
>>>> whenever pci_get_pdev_by_domain() returns NULL). That function as well
>>>> as pci_get_pdev_by_domain() use the passed in SBDF as if it was a
>>>> physical one; I'm unable to spot any translation. Yet I do recall
>>>> seeing assignment of a virtual device and function number somewhere
>>>> (perhaps another of the related series), so the model also doesn't
>>>> look to assume 1:1 mapping of SBDF.
>>> This question was answered by Oleksandr I think.
>> Yes; I continue to be sure though that I saw devfn allocation logic in
>> one of the many patches that are related here. And I'm relatively sure
>> that there no adjustment to logic here was made (but since it's hard
>> to pick the right patch out of the huge pile without knowing its title,
>> I can't reasonably go check).
> Offtop: I was somehow dropped from the Cc..
> 
> Please see:
> 
> [PATCH v3 10/11] vpci: Add initial support for virtual PCI bus topology
> [PATCH v3 11/11] xen/arm: Translate virtual PCI bus topology for guests
> 
> [1] https://patchwork.kernel.org/project/xen-devel/list/?series=555481

Ah yes, this way I can find them in my mailbox. And indeed - no translation
from virtual to physical SBDF on the config space read/write paths afaics.

Thanks for the pointer,
Jan