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

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>]

On 18.10.21 17:19, Jan Beulich wrote:
> 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://urldefense.com/v3/__https://patchwork.kernel.org/project/xen-devel/list/?series=555481__;!!GF_29dbcQIUBPA!mM8A39p8nk4UMK3YeKMMW9ua9BHj1UOWzaQcyx7G46YPdudxMpD3huqZfih0Uc8S-GyWXD_mPg$
>>  [patchwork[.]kernel[.]org]
> 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.
There are translations for both read and write [2] such as:

+    /*
+     * For the passed through devices we need to map their virtual SBDF
+     * to the physical PCI device being passed through.
+     */
+    if ( priv->is_virt_ecam && !pci_translate_virtual_device(v->domain, &sbdf) 
)
+            return 1;
+
>
> Thanks for the pointer,
> Jan
>
[2] 
https://patchwork.kernel.org/project/xen-devel/patch/20210930075223.860329-12-andr2000@xxxxxxxxx/