linux-kernel - Re: [PATCH v2 0/2] hyperv compose_msi

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Date:   Wed, 11 May 2022 17:51:26 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Jeffrey Hugo <quic_jhugo@...cinc.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, decui@...rosoft.com, lorenzo.pieralisi@....com,
        robh@...nel.org, kw@...ux.com, bhelgaas@...gle.com,
        jakeo@...rosoft.com, dazhan@...rosoft.com,
        linux-hyperv@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/2] hyperv compose_msi_msg fixups

On Wed, May 11, 2022 at 09:22:11AM -0600, Jeffrey Hugo wrote:
> While multi-MSI appears to work with pci-hyperv.c, there was a concern about
> how linux was doing the ITRE allocations.  Patch 2 addresses the concern.
> 
> However, patch 2 exposed an issue with how compose_msi_msg() was freeing a
> previous allocation when called for the Nth time.  Imagine a driver using
> pci_alloc_irq_vectors() to request 32 MSIs.  This would cause compose_msi_msg()
> to be called 32 times, once for each MSI.  With patch 2, MSI0 would allocate
> the ITREs needed, and MSI1-31 would use the cached information.  Then the driver
> uses request_irq() on MSI1-17.  This would call compose_msi_msg() again on those
> MSIs, which would again use the cached information.  Then unmask() would be
> called to retarget the MSIs to the right VCPU vectors.  Finally, the driver
> calls request_irq() on MSI0.  This would call conpose_msi_msg(), which would
> free the block of 32 MSIs, and allocate a new block.  This would undo the
> retarget of MSI1-17, and likely leave those MSIs targeting invalid VCPU vectors.
> This is addressed by patch 1, which is introduced first to prevent a regression.
> 
> Jeffrey Hugo (2):
>   PCI: hv: Reuse existing ITRE allocation in compose_msi_msg()
>   PCI: hv: Fix interrupt mapping for multi-MSI

Applied this version to hyperv-next. Thanks.