On 10.03.2025 10:55, Roger Pau Monne wrote:
> Attempt to reduce the MSI entry writes, and the associated checking whether
> memory decoding and MSI-X is enabled for the PCI device, when the MSI data
> hasn't changed.
>
> When using Interrupt Remapping the MSI entry will contain an index into
> the remapping table, and it's in such remapping table where the MSI vector
> and destination CPU is stored. As such, when using interrupt remapping,
> changes to the interrupt affinity shouldn't result in changes to the MSI
> entry, and the MSI entry update can be avoided.
>
> Signal from the IOMMU update_ire_from_msi hook whether the MSI data or
> address fields have changed, and thus need writing to the device registers.
> Such signaling is done by returning 1 from the function. Otherwise
> returning 0 means no update of the MSI fields, and thus no write
> required.
>
> Signed-off-by: Roger Pau Monné <roger....@citrix.com>
Reviewed-by: Jan Beulich <jbeul...@suse.com>
with two purely cosmetic suggestions and an only loosely related question below.
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -415,7 +415,9 @@ static int cf_check vmx_pi_update_irte(const struct vcpu
> *v,
>
> ASSERT_PDEV_LIST_IS_READ_LOCKED(msi_desc->dev->domain);
>
> - return iommu_update_ire_from_msi(msi_desc, &msi_desc->msg);
> + rc = iommu_update_ire_from_msi(msi_desc, &msi_desc->msg);
> +
> + return rc < 0 ? rc : 0;
Only tangential here, but: Why does this function have a return type of
non-void, when neither caller cares?
> --- a/xen/drivers/passthrough/amd/iommu_intr.c
> +++ b/xen/drivers/passthrough/amd/iommu_intr.c
> @@ -492,7 +492,7 @@ static int update_intremap_entry_from_msi_msg(
> get_ivrs_mappings(iommu->seg)[alias_id].intremap_table);
> }
>
> - return 0;
> + return !fresh ? 0 : 1;
> }
Simply
return fresh;
?
> @@ -546,7 +546,7 @@ int cf_check amd_iommu_msi_msg_update_ire(
> rc = update_intremap_entry_from_msi_msg(iommu, bdf, nr,
> &msi_desc->remap_index,
> msg, &data);
> - if ( !rc )
> + if ( rc > 0 )
> {
> for ( i = 1; i < nr; ++i )
> msi_desc[i].remap_index = msi_desc->remap_index + i;
> --- a/xen/drivers/passthrough/vtd/intremap.c
> +++ b/xen/drivers/passthrough/vtd/intremap.c
> @@ -506,6 +506,7 @@ static int msi_msg_to_remap_entry(
> unsigned int index, i, nr = 1;
> unsigned long flags;
> const struct pi_desc *pi_desc = msi_desc->pi_desc;
> + bool alloc = false;
>
> if ( msi_desc->msi_attrib.type == PCI_CAP_ID_MSI )
> nr = msi_desc->msi.nvec;
> @@ -529,6 +530,7 @@ static int msi_msg_to_remap_entry(
> index = alloc_remap_entry(iommu, nr);
> for ( i = 0; i < nr; ++i )
> msi_desc[i].remap_index = index + i;
> + alloc = true;
> }
> else
> index = msi_desc->remap_index;
> @@ -601,7 +603,7 @@ static int msi_msg_to_remap_entry(
> unmap_vtd_domain_page(iremap_entries);
> spin_unlock_irqrestore(&iommu->intremap.lock, flags);
>
> - return 0;
> + return alloc ? 1 : 0;
> }
Like above, simply
return alloc;
?
Jan
