RE: [PATCH 2/2] PCI: hv: Fix interrupt mapping for multi-MSI

[Dexuan Cui]

> From: Jeffrey Hugo <quic_jhugo@xxxxxxxxxxx>
> Sent: Monday, May 9, 2022 2:48 PM
> ...
> According to Dexuan, the hypervisor folks beleive that multi-msi
> allocations are not correct.  compose_msi_msg() will allocate multi-msi
> one by one.  However, multi-msi is a block of related MSIs, with alignment
> requirements.  In order for the hypervisor to allocate properly aligned
> and consecutive entries in the IOMMU Interrupt Remapping Table, there
> should be a single mapping request that requests all of the multi-msi
> vectors in one shot.
> 
> Dexuan suggests detecting the multi-msi case and composing a single
> request related to the first MSI.  Then for the other MSIs in the same
> block, use the cached information.  This appears to be viable, so do it.
> 
> Suggested-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> Signed-off-by: Jeffrey Hugo <quic_jhugo@xxxxxxxxxxx>

Reviewed-by: Dexuan Cui <decui@xxxxxxxxxxxxx>

> +	if (!msi_desc->pci.msi_attrib.is_msix && msi_desc->nvec_used > 1) {
> +		/*
> +		 * if this is not the first MSI of Multi MSI, we already have

s/if/If