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Date:   Thu, 28 Apr 2022 15:08:19 +0000
From:   Wei Liu <wei.liu@kernel.org>
To:     Jeffrey Hugo <quic_jhugo@quicinc.com>
Cc:     Wei Liu <wei.liu@kernel.org>, kys@microsoft.com,
        haiyangz@microsoft.com, sthemmin@microsoft.com,
        decui@microsoft.com, lorenzo.pieralisi@arm.com, robh@kernel.org,
        kw@linux.com, bhelgaas@google.com, bjorn.andersson@linaro.org,
        linux-hyperv@vger.kernel.org, linux-pci@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] PCI: hv: Fix hv_arch_irq_unmask() for multi-MSI
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On Thu, Apr 28, 2022 at 09:06:42AM -0600, Jeffrey Hugo wrote:
> On 4/28/2022 8:58 AM, Wei Liu wrote:
> > On Wed, Apr 27, 2022 at 08:07:33AM -0600, Jeffrey Hugo wrote:
> > > In the multi-MSI case, hv_arch_irq_unmask() will only operate on the first
> > > MSI of the N allocated.  This is because only the first msi_desc is cached
> > > and it is shared by all the MSIs of the multi-MSI block.  This means that
> > > hv_arch_irq_unmask() gets the correct address, but the wrong data (always
> > > 0).
> > > 
> > > This can break MSIs.
> > > 
> > > Lets assume MSI0 is vector 34 on CPU0, and MSI1 is vector 33 on CPU0.
> > > 
> > > hv_arch_irq_unmask() is called on MSI0.  It uses a hypercall to configure
> > > the MSI address and data (0) to vector 34 of CPU0.  This is correct.  Then
> > > hv_arch_irq_unmask is called on MSI1.  It uses another hypercall to
> > > configure the MSI address and data (0) to vector 33 of CPU0.  This is
> > > wrong, and results in both MSI0 and MSI1 being routed to vector 33.  Linux
> > > will observe extra instances of MSI1 and no instances of MSI0 despite the
> > > endpoint device behaving correctly.
> > > 
> > > For the multi-MSI case, we need unique address and data info for each MSI,
> > > but the cached msi_desc does not provide that.  However, that information
> > > can be gotten from the int_desc cached in the chip_data by
> > > compose_msi_msg().  Fix the multi-MSI case to use that cached information
> > > instead.  Since hv_set_msi_entry_from_desc() is no longer applicable,
> > > remove it.
> > > 
> > > Signed-off-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
> > > ---
> > >   drivers/pci/controller/pci-hyperv.c | 12 ++++--------
> > >   1 file changed, 4 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> > > index 5800ecf..7aea0b7 100644
> > > --- a/drivers/pci/controller/pci-hyperv.c
> > > +++ b/drivers/pci/controller/pci-hyperv.c
> > > @@ -611,13 +611,6 @@ static unsigned int hv_msi_get_int_vector(struct irq_data *data)
> > >   	return cfg->vector;
> > >   }
> > > -static void hv_set_msi_entry_from_desc(union hv_msi_entry *msi_entry,
> > > -				       struct msi_desc *msi_desc)
> > > -{
> > > -	msi_entry->address.as_uint32 = msi_desc->msg.address_lo;
> > > -	msi_entry->data.as_uint32 = msi_desc->msg.data;
> > > -}
> > > -
> > 
> > Instead of dropping this function, can you change the second argument to
> > take struct tran_int_desc *?
> > 
> > This way you can use the same function in hv_compose_msi_msg.
> 
> I do not see how this could be reused in hv_compose_msi_msg() with the
> proposed change of the second argument.  The hv_msi_entry type is not used
> in hv_compose_msi_msg(), nor does it look like it is applicable anywhere
> within the function.
> 
> What am I missing?

I mixed up two different types while going through the code --
hv_msi_entry and Linux's own msi_entry type. Sorry for the noise.

Wei.