Re: [PATCH] KVM: Add system call KVM_VERIFY_MSI to verify MSI vector

[chenxiang (M)]

Hi Marc,


在 2022/11/8 20:47, Marc Zyngier 写道:
> On Tue, 08 Nov 2022 08:08:57 +0000,
> chenxiang <chenxiang66@hisilicon.com> wrote:
> > From: Xiang Chen <chenxiang66@hisilicon.com>
> >
> > Currently the numbers of MSI vectors come from register PCI_MSI_FLAGS
> > which should be power-of-2, but in some scenaries it is not the same as
> > the number that driver requires in guest, for example, a PCI driver wants
> > to allocate 6 MSI vecotrs in guest, but as the limitation, it will allocate
> > 8 MSI vectors. So it requires 8 MSI vectors in qemu while the driver in
> > guest only wants to allocate 6 MSI vectors.
> >
> > When GICv4.1 is enabled, we can see some exception print as following for
> > above scenaro:
> > vfio-pci 0000:3a:00.1: irq bypass producer (token 000000008f08224d) 
> > registration fails:66311
> >
> > In order to verify whether a MSI vector is valid, add KVM_VERIFY_MSI to do
> > that. If there is a mapping, return 0, otherwise return negative value.
> >
> > This is the kernel part of adding system call KVM_VERIFY_MSI.
> Exposing something that is an internal implementation detail to
> userspace feels like the absolute wrong way to solve this issue.
>
> Can you please characterise the issue you're having? Is it that vfio
> tries to enable an interrupt for which there is no virtual ITS
> mapping? Shouldn't we instead try and manage this in the kernel?

Before i reported the issue to community, you gave a suggestion about 
the issue, but not sure whether i misundertood your meaning.
You can refer to the link for more details about the issue.
https://lkml.kernel.org/lkml/87cze9lcut.wl-maz@kernel.org/T/

Best regards,
Xiang