Re: [PATCH v3 0/3] x86/IOMMU: multi-vector MSI prerequisites

[Suravee Suthikulanit <suravee.suthikulpanit@amd.com>]

On 4/16/2013 1:43 AM, Jan Beulich wrote:
>> On another topic, in arch/x86/msi.c, in the function
>> >"setup_msi_affinity()", the code does:
>> >1. "read_msi_msg"
>> >2. Modify the affitity mask
>> >3. "write_msi_msg" back the register value.
>> >
>> >In read, if the interrupt remapping is enabled, from the patch, the
>> >function returns the MSI data with remapped information from IOMMU. Then
>> >in write, if the interrupt remapping is enabled, the function will
>> >update the IOMMU interrupt remapping entries with the already "remapped"
>> >vector.   In this case, you would be updating the incorrect IOMMU IRTE.
> Where did you spot that?
This is in xen/arch/x86/msi.c

> To prevent this from happening is exactly
> why amd_iommu_read_msi_from_ire() isn't empty anymore (this is
> where the original MSI message information gets reconstructed - or
> at least is intended to be). The only modification done by
> update_intremap_entry_from_msi_msg() are the low 11 data bits,
> and that's what gets overwritten upon read.
Sorry, I am not quite following this.  Why do we need to reconstruct MSI 
message? Why was  not it required in the past?

Suravee.