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Re: [PATCH v12.2 01/15] vpci: use per-domain PCI lock to protect vpci structure
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>
- From: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
- Date: Wed, 24 Jan 2024 00:00:44 -0500
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- Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Jun Nakajima <jun.nakajima@xxxxxxxxx>, Kevin Tian <kevin.tian@xxxxxxxxx>, Paul Durrant <paul@xxxxxxx>, Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 24 Jan 2024 05:01:07 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 1/23/24 10:07, Roger Pau Monné wrote:
> On Tue, Jan 23, 2024 at 03:32:12PM +0100, Jan Beulich wrote:
>> On 15.01.2024 20:43, Stewart Hildebrand wrote:
>>> @@ -2888,6 +2888,8 @@ int allocate_and_map_msi_pirq(struct domain *d, int
>>> index, int *pirq_p,
>>> {
>>> int irq, pirq, ret;
>>>
>>> + ASSERT(pcidevs_locked() || rw_is_locked(&d->pci_lock));
>>
>> If either lock is sufficient to hold here, ...
>>
>>> --- a/xen/arch/x86/physdev.c
>>> +++ b/xen/arch/x86/physdev.c
>>> @@ -123,7 +123,9 @@ int physdev_map_pirq(domid_t domid, int type, int
>>> *index, int *pirq_p,
>>>
>>> case MAP_PIRQ_TYPE_MSI:
>>> case MAP_PIRQ_TYPE_MULTI_MSI:
>>> + pcidevs_lock();
>>> ret = allocate_and_map_msi_pirq(d, *index, pirq_p, type, msi);
>>> + pcidevs_unlock();
>>> break;
>>
>> ... why is it the global lock that's being acquired here?
>>
>
> IIRC (Stewart can further comment) this is done holding the pcidevs
> lock to keep the path unmodified, as there's no need to hold the
> per-domain rwlock.
>
Although allocate_and_map_msi_pirq() was itself acquiring the global
pcidevs_lock() before this patch, we could just as well use
read_lock(&d->pci_lock) here instead now. It seems like a good optimization to
make, so if there aren't any objections I'll change it to
read_lock(&d->pci_lock).
|
