x86/mm/iommu/sva: Make LAM and SVA mutually exclusive

IOMMU and SVA-capable devices know nothing about LAM and only expect
canonical addresses. An attempt to pass down tagged pointer will lead
to address translation failure.

By default do not allow to enable both LAM and use SVA in the same
process.

The new ARCH_FORCE_TAGGED_SVA arch_prctl() overrides the limitation.
By using the arch_prctl() userspace takes responsibility to never pass
tagged address to the device.

Signed-off-by: Kirill A. Shutemov <[email protected]>
Signed-off-by: Dave Hansen <[email protected]>
Reviewed-by: Ashok Raj <[email protected]>
Reviewed-by: Jacob Pan <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lore.kernel.org/all/20230312112612.31869-12-kirill.shutemov%40linux.intel.com

Author: kiryl

arch/x86/include/asm/mmu.h

@@ -14,6 +14,8 @@
 #define MM_CONTEXT_HAS_VSYSCALL		1
 /* Do not allow changing LAM mode */
 #define MM_CONTEXT_LOCK_LAM		2
+/* Allow LAM and SVA coexisting */
+#define MM_CONTEXT_FORCE_TAGGED_SVA	3
 
 /*
  * x86 has arch-specific MMU state beyond what lives in mm_struct.

arch/x86/include/asm/mmu_context.h

@@ -115,6 +115,12 @@ static inline void mm_reset_untag_mask(struct mm_struct *mm)
 	mm->context.untag_mask = -1UL;
 }
 
+#define arch_pgtable_dma_compat arch_pgtable_dma_compat
+static inline bool arch_pgtable_dma_compat(struct mm_struct *mm)
+{
+	return !mm_lam_cr3_mask(mm) ||
+		test_bit(MM_CONTEXT_FORCE_TAGGED_SVA, &mm->context.flags);
+}
 #else
 
 static inline unsigned long mm_lam_cr3_mask(struct mm_struct *mm)

arch/x86/include/uapi/asm/prctl.h

@@ -23,5 +23,6 @@
 #define ARCH_GET_UNTAG_MASK		0x4001
 #define ARCH_ENABLE_TAGGED_ADDR		0x4002
 #define ARCH_GET_MAX_TAG_BITS		0x4003
+#define ARCH_FORCE_TAGGED_SVA		0x4004
 
 #endif /* _ASM_X86_PRCTL_H */

arch/x86/kernel/process_64.c

@@ -756,6 +756,10 @@ static int prctl_enable_tagged_addr(struct mm_struct *mm, unsigned long nr_bits)
 	if (current->mm != mm)
 		return -EINVAL;
 
+	if (mm_valid_pasid(mm) &&
+	    !test_bit(MM_CONTEXT_FORCE_TAGGED_SVA, &mm->context.flags))
+		return -EINTR;
+
 	if (mmap_write_lock_killable(mm))
 		return -EINTR;
 
@@ -878,6 +882,9 @@ long do_arch_prctl_64(struct task_struct *task, int option, unsigned long arg2)
 				(unsigned long __user *)arg2);
 	case ARCH_ENABLE_TAGGED_ADDR:
 		return prctl_enable_tagged_addr(task->mm, arg2);
+	case ARCH_FORCE_TAGGED_SVA:
+		set_bit(MM_CONTEXT_FORCE_TAGGED_SVA, &task->mm->context.flags);
+		return 0;
 	case ARCH_GET_MAX_TAG_BITS:
 		if (!cpu_feature_enabled(X86_FEATURE_LAM))
 			return put_user(0, (unsigned long __user *)arg2);

drivers/iommu/iommu-sva.c

@@ -2,6 +2,7 @@
 /*
  * Helpers for IOMMU drivers implementing SVA
  */
+#include <linux/mmu_context.h>
 #include <linux/mutex.h>
 #include <linux/sched/mm.h>
 #include <linux/iommu.h>
@@ -32,6 +33,9 @@ int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max)
 	    min == 0 || max < min)
 		return -EINVAL;
 
+	if (!arch_pgtable_dma_compat(mm))
+		return -EBUSY;
+
 	mutex_lock(&iommu_sva_lock);
 	/* Is a PASID already associated with this mm? */
 	if (mm_valid_pasid(mm)) {

include/linux/mmu_context.h

@@ -35,4 +35,11 @@ static inline unsigned long mm_untag_mask(struct mm_struct *mm)
 }
 #endif
 
+#ifndef arch_pgtable_dma_compat
+static inline bool arch_pgtable_dma_compat(struct mm_struct *mm)
+{
+	return true;
+}
+#endif
+
 #endif