Re: [PATCH v6 3/7] xen/arm: setup MMIO range trap handlers for hardware domain

From: Oleksandr Andrushchenko <Oleksandr_Andrushchenko@epam.com>
To: Julien Grall <julien@xen.org>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: "sstabellini@kernel.org" <sstabellini@kernel.org>,
	Oleksandr Tyshchenko <Oleksandr_Tyshchenko@epam.com>,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>,
	Artem Mygaiev <Artem_Mygaiev@epam.com>,
	"roger.pau@citrix.com" <roger.pau@citrix.com>,
	"jbeulich@suse.com" <jbeulich@suse.com>,
	"andrew.cooper3@citrix.com" <andrew.cooper3@citrix.com>,
	"george.dunlap@citrix.com" <george.dunlap@citrix.com>,
	"paul@xen.org" <paul@xen.org>,
	Bertrand Marquis <bertrand.marquis@arm.com>,
	Rahul Singh <rahul.singh@arm.com>
Subject: Re: [PATCH v6 3/7] xen/arm: setup MMIO range trap handlers for hardware domain
Date: Wed, 24 Nov 2021 07:22:20 +0000	[thread overview]
Message-ID: <997b74fc-0a74-80b3-1fa7-dbf38ebddfbd@epam.com> (raw)
In-Reply-To: <12447bb3-e3b4-c1f3-17f7-09704fd8b847@xen.org>

Hi, Julien!

On 23.11.21 18:58, Julien Grall wrote:
> Hi,
>
> On 23/11/2021 16:41, Oleksandr Andrushchenko wrote:
>> On 23.11.21 18:12, Julien Grall wrote:
>>> On 23/11/2021 06:58, Oleksandr Andrushchenko wrote:
>>>> unsigned int domain_vpci_get_num_mmio_handlers(struct domain *d)
>>>> {
>>>>        if ( !has_vpci(d) )
>>>>            return 0;
>>>>
>>>>        if ( is_hardware_domain(d) )
>>>>        {
>>>>            int ret = pci_host_iterate_bridges_and_count(d, vpci_get_num_handlers_cb);
>>>>
>>>>            return ret < 0 ? 0 : ret;
>>>>        }
>>>>
>>>>        /*
>>>>         * This is a guest domain:
>>>>         *
>>>>         * 1 for a single emulated host bridge's configuration space.
>>>>         */
>>>>        return 1;
>>>
>>> I am afraid that my question stands even with this approach. This patch is only meant to handle the hardware domain, therefore the change seems to be out of context.
>>>
>>> I would prefer if this change is done separately.
>> While I do agree that MSI part and virtual bus topology are not belonging to this
>> patch I can't agree with the rest: we already have MMIO handlers for guest domains
>> and we introduce domain_vpci_get_num_mmio_handlers which must also account
>> on guests and stay consistent.
>> So, despite the patch has "hardware domain" in its name it doesn't mean we should
>> break guests here.
>
> We were already registering the handler for guest domain before your patch. So this is nothing new.
>
> At the moment, we always allocate an extra 16 slot for IO handlers (see MAX_IO_HANDLER). So we are not breaking anything. Instead, this is simply a latent bug.
Agree
>
>> Thus I do think the above is still correct wrt this patch.
>
> The idea of splitting patch is to separate bug fix from new code. This helps backporting and review.
>
> In this case, we don't care about backport (PCI passthrough is no supported) and the fix a simple enough. So I am not going to insist on splitting to a separate patch.
>
> However, this change *must* be explained in the commit message.
I will add a dedicated patch to fix that
>
> Cheers,
>
Thank you,
Oleksandr