2023-10-26 08:54:18

by Lu Baolu

Subject: [PATCH 1/1] iommu: Avoid unnecessary cache invalidations

The iommu_create_device_direct_mappings() only needs to flush the caches
when the mappings are changed in the affected domain. This is not true
for non-DMA domains, or for devices attached to the domain that have no
reserved regions. To avoid unnecessary cache invalidations, add a check
before iommu_flush_iotlb_all().

Fixes: a48ce36e2786 ("iommu: Prevent RESV_DIRECT devices from blocking domains")
Signed-off-by: Lu Baolu <[email protected]>
---
drivers/iommu/iommu.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 00d0a2b5d7dc..0cb676590bfa 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1114,7 +1114,8 @@ static int iommu_create_device_direct_mappings(struct iommu_domain *domain,

}

- iommu_flush_iotlb_all(domain);
+ if (!list_empty(&mappings) && iommu_is_dma_domain(domain))
+ iommu_flush_iotlb_all(domain);

out:
iommu_put_resv_regions(dev, &mappings);
--
2.34.1

2023-10-27 04:31:45

by Henry Willard

Subject: Re: [PATCH 1/1] iommu: Avoid unnecessary cache invalidations

On Oct 26, 2023, at 1:49 AM, Lu Baolu <[email protected]> wrote:
>
> The iommu_create_device_direct_mappings() only needs to flush the caches
> when the mappings are changed in the affected domain. This is not true
> for non-DMA domains, or for devices attached to the domain that have no
> reserved regions. To avoid unnecessary cache invalidations, add a check
> before iommu_flush_iotlb_all().

This also fixes a boot failure on Sapphire Rapids built with
CONFIG_IOMMU_DEFAULT_PASSTHROUGH=y or the equivalent via
kernel command line parameters.

>
> Fixes: a48ce36e2786 ("iommu: Prevent RESV_DIRECT devices from blocking domains")
> Signed-off-by: Lu Baolu <[email protected]>
Tested-by: Henry Willard <[email protected]>
> ---
> drivers/iommu/iommu.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 00d0a2b5d7dc..0cb676590bfa 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1114,7 +1114,8 @@ static int iommu_create_device_direct_mappings(struct iommu_domain *domain,
>
> }
>
> - iommu_flush_iotlb_all(domain);
> + if (!list_empty(&mappings) && iommu_is_dma_domain(domain))
> + iommu_flush_iotlb_all(domain);
>
> out:
> iommu_put_resv_regions(dev, &mappings);
> --
> 2.34.1
>
>

2023-10-27 06:57:53

by Joerg Roedel

Subject: Re: [PATCH 1/1] iommu: Avoid unnecessary cache invalidations

On Thu, Oct 26, 2023 at 04:49:42PM +0800, Lu Baolu wrote:
> The iommu_create_device_direct_mappings() only needs to flush the caches
> when the mappings are changed in the affected domain. This is not true
> for non-DMA domains, or for devices attached to the domain that have no
> reserved regions. To avoid unnecessary cache invalidations, add a check
> before iommu_flush_iotlb_all().
>
> Fixes: a48ce36e2786 ("iommu: Prevent RESV_DIRECT devices from blocking domains")
> Signed-off-by: Lu Baolu <[email protected]>
> ---
> drivers/iommu/iommu.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)

Applied, thanks.