[xen staging] iommu/ipmmu-vmsa: Use refcount for the micro-TLBs

[patchbot@xxxxxxx]

commit c52af96fdcac9eff31465f39c0ffcceadca9ac9f
Author:     Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
AuthorDate: Thu Jan 27 21:55:51 2022 +0200
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Mon Jan 31 18:33:20 2022 +0000

    iommu/ipmmu-vmsa: Use refcount for the micro-TLBs
    
    Reference-count the micro-TLBs as several bus masters can be
    connected to the same micro-TLB (and drop TODO comment).
    This wasn't an issue so far, since the platform devices
    (this driver deals with) get assigned/deassigned together during
    domain creation/destruction. But, in order to support PCI devices
    (which are hot-pluggable) in the near future we will need to
    take care of.
    
    Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
    Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
---
 xen/drivers/passthrough/arm/ipmmu-vmsa.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/xen/drivers/passthrough/arm/ipmmu-vmsa.c 
b/xen/drivers/passthrough/arm/ipmmu-vmsa.c
index 649b9f6362..c912120411 100644
--- a/xen/drivers/passthrough/arm/ipmmu-vmsa.c
+++ b/xen/drivers/passthrough/arm/ipmmu-vmsa.c
@@ -127,6 +127,7 @@ struct ipmmu_vmsa_device {
     spinlock_t lock;    /* Protects ctx and domains[] */
     DECLARE_BITMAP(ctx, IPMMU_CTX_MAX);
     struct ipmmu_vmsa_domain *domains[IPMMU_CTX_MAX];
+    unsigned int utlb_refcount[IPMMU_UTLB_MAX];
     const struct ipmmu_features *features;
 };
 
@@ -468,12 +469,17 @@ static int ipmmu_utlb_enable(struct ipmmu_vmsa_domain 
*domain,
     }
 
     /*
-     * TODO: Reference-count the micro-TLB as several bus masters can be
-     * connected to the same micro-TLB.
+     * Reference-count the micro-TLBs as several bus masters can be connected
+     * to the same micro-TLB. The platform devices get assigned/deassigned
+     * together during domain creation/destruction. The PCI devices which use
+     * the same micro-TLB must also be hot-(un)plugged together.
      */
-    ipmmu_imuasid_write(mmu, utlb, 0);
-    ipmmu_imuctr_write(mmu, utlb, imuctr |
-                       IMUCTR_TTSEL_MMU(domain->context_id) | IMUCTR_MMUEN);
+    if ( mmu->utlb_refcount[utlb]++ == 0 )
+    {
+        ipmmu_imuasid_write(mmu, utlb, 0);
+        ipmmu_imuctr_write(mmu, utlb, imuctr |
+                           IMUCTR_TTSEL_MMU(domain->context_id) | 
IMUCTR_MMUEN);
+    }
 
     return 0;
 }
@@ -484,7 +490,10 @@ static void ipmmu_utlb_disable(struct ipmmu_vmsa_domain 
*domain,
 {
     struct ipmmu_vmsa_device *mmu = domain->mmu;
 
-    ipmmu_imuctr_write(mmu, utlb, 0);
+    ASSERT(mmu->utlb_refcount[utlb] > 0);
+
+    if ( --mmu->utlb_refcount[utlb] == 0 )
+        ipmmu_imuctr_write(mmu, utlb, 0);
 }
 
 /* Domain/Context Management */
--
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