x86/mmu: Allocate/free a PASID

A PASID is allocated for an "mm" the first time any thread binds to an
SVA-capable device and is freed from the "mm" when the SVA is unbound
by the last thread. It's possible for the "mm" to have different PASID
values in different binding/unbinding SVA cycles.

The mm's PASID (non-zero for valid PASID or 0 for invalid PASID) is
propagated to a per-thread PASID MSR for all threads within the mm
through IPI, context switch, or inherited. This is done to ensure that a
running thread has the right PASID in the MSR matching the mm's PASID.

 [ bp: s/SVM/SVA/g; massage. ]

Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/1600187413-163670-10-git-send-email-fenghua.yu@intel.com

1 files changed, 27 insertions, 1 deletions

diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
index fc90a079e228..60ffe083b6d6 100644
--- a/drivers/iommu/intel/svm.c
+++ b/drivers/iommu/intel/svm.c
@@ -19,6 +19,7 @@
 #include <linux/mm_types.h>
 #include <linux/ioasid.h>
 #include <asm/page.h>
+#include <asm/fpu/api.h>
 
 #include "pasid.h"
 
@@ -444,6 +445,24 @@ out:
 	return ret;
 }
 
+static void _load_pasid(void *unused)
+{
+	update_pasid();
+}
+
+static void load_pasid(struct mm_struct *mm, u32 pasid)
+{
+	mutex_lock(&mm->context.lock);
+
+	/* Synchronize with READ_ONCE in update_pasid(). */
+	smp_store_release(&mm->pasid, pasid);
+
+	/* Update PASID MSR on all CPUs running the mm's tasks. */
+	on_each_cpu_mask(mm_cpumask(mm), _load_pasid, NULL, true);
+
+	mutex_unlock(&mm->context.lock);
+}
+
 /* Caller must hold pasid_mutex, mm reference */
 static int
 intel_svm_bind_mm(struct device *dev, unsigned int flags,
@@ -591,6 +610,10 @@ intel_svm_bind_mm(struct device *dev, unsigned int flags,
 		}
 
 		list_add_tail(&svm->list, &global_svm_list);
+		if (mm) {
+			/* The newly allocated pasid is loaded to the mm. */
+			load_pasid(mm, svm->pasid);
+		}
 	} else {
 		/*
 		 * Binding a new device with existing PASID, need to setup
@@ -654,8 +677,11 @@ static int intel_svm_unbind_mm(struct device *dev, u32 pasid)
 
 			if (list_empty(&svm->devs)) {
 				ioasid_free(svm->pasid);
-				if (svm->mm)
+				if (svm->mm) {
 					mmu_notifier_unregister(&svm->notifier, svm->mm);
+					/* Clear mm's pasid. */
+					load_pasid(svm->mm, PASID_DISABLED);
+				}
 				list_del(&svm->list);
 				/* We mandate that no page faults may be outstanding
 				 * for the PASID when intel_svm_unbind_mm() is called.