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

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Date:   Wed, 11 May 2022 11:53:49 -0600
From:   Jeffrey Hugo <quic_jhugo@...cinc.com>
To:     Wei Liu <wei.liu@...nel.org>
CC:     <kys@...rosoft.com>, <haiyangz@...rosoft.com>,
        <sthemmin@...rosoft.com>, <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 5/11/2022 11:51 AM, Wei Liu wrote:
> 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.

Thanks for picking it up.  Sorry about the confusion.