[PATCH] iommu/amd: Tidy up DMA ops init

[PATCH] iommu/amd: Tidy up DMA ops init

[Robin Murphy]

Now that DMA ops are part of the core API via iommu-dma, fold the
vestigial remains of the IOMMU_DMA_OPS init state into the IOMMU API
phase, and clean up a few other leftovers. This should also close the
race window wherein bus_set_iommu() effectively makes the DMA ops state
visible before its nominal initialisation - it seems this was previously
fairly benign, but since commit a250c23f15c2 ("iommu: remove
DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE") it can now lead to the strict flush
queue policy inadvertently being picked for default domains allocated
during that window, with a corresponding unexpected perfomance impact.

Reported-by: Jussi Maki <joamaki@gmail.com>
Tested-by: Jussi Maki <joamaki@gmail.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>

---

As discussed on the report thread, I think it makes most sense to merge
this as a fix for 5.13 and not worry about any backporting.

 drivers/iommu/amd/amd_iommu.h |  2 --
 drivers/iommu/amd/init.c      |  5 -----
 drivers/iommu/amd/iommu.c     | 31 +++++++++++++------------------
 3 files changed, 13 insertions(+), 25 deletions(-)

diff --git a/drivers/iommu/amd/amd_iommu.h b/drivers/iommu/amd/amd_iommu.h
index 55dd38d814d9..416815a525d6 100644
--- a/drivers/iommu/amd/amd_iommu.h
+++ b/drivers/iommu/amd/amd_iommu.h
@@ -11,8 +11,6 @@
 
 #include "amd_iommu_types.h"
 
-extern int amd_iommu_init_dma_ops(void);
-extern int amd_iommu_init_passthrough(void);
 extern irqreturn_t amd_iommu_int_thread(int irq, void *data);
 extern irqreturn_t amd_iommu_int_handler(int irq, void *data);
 extern void amd_iommu_apply_erratum_63(u16 devid);
diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index d006724f4dc2..a418bf560a4b 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -231,7 +231,6 @@ enum iommu_init_state {
 	IOMMU_ENABLED,
 	IOMMU_PCI_INIT,
 	IOMMU_INTERRUPTS_EN,
-	IOMMU_DMA_OPS,
 	IOMMU_INITIALIZED,
 	IOMMU_NOT_FOUND,
 	IOMMU_INIT_ERROR,
@@ -2895,10 +2894,6 @@ static int __init state_next(void)
 		init_state = ret ? IOMMU_INIT_ERROR : IOMMU_INTERRUPTS_EN;
 		break;
 	case IOMMU_INTERRUPTS_EN:
-		ret = amd_iommu_init_dma_ops();
-		init_state = ret ? IOMMU_INIT_ERROR : IOMMU_DMA_OPS;
-		break;
-	case IOMMU_DMA_OPS:
 		init_state = IOMMU_INITIALIZED;
 		break;
 	case IOMMU_INITIALIZED:
diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 80e8e1916dd1..2efe6d17783c 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -30,7 +30,6 @@
 #include <linux/msi.h>
 #include <linux/irqdomain.h>
 #include <linux/percpu.h>
-#include <linux/iova.h>
 #include <linux/io-pgtable.h>
 #include <asm/irq_remapping.h>
 #include <asm/io_apic.h>
@@ -1771,13 +1770,22 @@ void amd_iommu_domain_update(struct protection_domain *domain)
 	amd_iommu_domain_flush_complete(domain);
 }
 
+static void __init amd_iommu_init_dma_ops(void)
+{
+	swiotlb = (iommu_default_passthrough() || sme_me_mask) ? 1 : 0;
+
+	if (amd_iommu_unmap_flush)
+		pr_info("IO/TLB flush on unmap enabled\n");
+	else
+		pr_info("Lazy IO/TLB flushing enabled\n");
+	iommu_set_dma_strict(amd_iommu_unmap_flush);
+}
+
 int __init amd_iommu_init_api(void)
 {
-	int ret, err = 0;
+	int err = 0;
 
-	ret = iova_cache_get();
-	if (ret)
-		return ret;
+	amd_iommu_init_dma_ops();
 
 	err = bus_set_iommu(&pci_bus_type, &amd_iommu_ops);
 	if (err)
@@ -1794,19 +1802,6 @@ int __init amd_iommu_init_api(void)
 	return 0;
 }
 
-int __init amd_iommu_init_dma_ops(void)
-{
-	swiotlb        = (iommu_default_passthrough() || sme_me_mask) ? 1 : 0;
-
-	if (amd_iommu_unmap_flush)
-		pr_info("IO/TLB flush on unmap enabled\n");
-	else
-		pr_info("Lazy IO/TLB flushing enabled\n");
-	iommu_set_dma_strict(amd_iommu_unmap_flush);
-	return 0;
-
-}
-
 /*****************************************************************************
  *
  * The following functions belong to the exported interface of AMD IOMMU
-- 
2.21.0.dirty

Re: [PATCH] iommu/amd: Tidy up DMA ops init

[Joerg Roedel]

On Thu, Jun 03, 2021 at 02:48:21PM +0100, Robin Murphy wrote:
> As discussed on the report thread, I think it makes most sense to merge
> this as a fix for 5.13 and not worry about any backporting.
> 
>  drivers/iommu/amd/amd_iommu.h |  2 --
>  drivers/iommu/amd/init.c      |  5 -----
>  drivers/iommu/amd/iommu.c     | 31 +++++++++++++------------------
>  3 files changed, 13 insertions(+), 25 deletions(-)

Applied for v5.13, thanks Robin et al for the quick work on this
regression.

Robin, do you by chance have a Fixes tag which I can add?

Thanks,

	Joerg

Re: [PATCH] iommu/amd: Tidy up DMA ops init

[Robin Murphy]

On 2021-06-04 16:26, Joerg Roedel wrote:
> On Thu, Jun 03, 2021 at 02:48:21PM +0100, Robin Murphy wrote:
>> As discussed on the report thread, I think it makes most sense to merge
>> this as a fix for 5.13 and not worry about any backporting.
>>
>>   drivers/iommu/amd/amd_iommu.h |  2 --
>>   drivers/iommu/amd/init.c      |  5 -----
>>   drivers/iommu/amd/iommu.c     | 31 +++++++++++++------------------
>>   3 files changed, 13 insertions(+), 25 deletions(-)
> 
> Applied for v5.13, thanks Robin et al for the quick work on this
> regression.
> 
> Robin, do you by chance have a Fixes tag which I can add?

For the sake of justifying this as "fix" rather than "cleanup", you may 
as well use the flush queue commit cited in the patch log - I maintain 
there's nothing technically wrong with that commit itself, but it is the 
point at which the underlying issue becomes worth fixing due to how they 
interact ;)

Cheers,
Robin.

Re: [PATCH] iommu/amd: Tidy up DMA ops init

[Joerg Roedel]

On Fri, Jun 04, 2021 at 06:35:17PM +0100, Robin Murphy wrote:
> For the sake of justifying this as "fix" rather than "cleanup", you may as
> well use the flush queue commit cited in the patch log - I maintain there's
> nothing technically wrong with that commit itself, but it is the point at
> which the underlying issue becomes worth fixing due to how they interact ;)

Okay :) I added:

Fixes: a250c23f15c2 ("iommu: remove DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE")

Regards,

	Joerg