powerpc/mm: Add tracking of the number of coprocessors using a context

commit aff6f8cb3e2170b9e58b0932bce7bfb492775e23 upstream.

Currently, when using coprocessors (which use the Nest MMU), we
simply increment the active_cpu count to force all TLB invalidations
to be come broadcast.

Unfortunately, due to an errata in POWER9, we will need to know
more specifically that coprocessors are in use.

This maintains a separate copros counter in the MMU context for
that purpose.

NB. The commit mentioned in the fixes tag below is not at fault for
the bug we're fixing in this commit and the next, but this fix applies
on top the infrastructure it introduced.

Fixes: 03b8abedf4f4 ("cxl: Enable global TLBIs for cxl contexts")
Cc: stable@vger.kernel.org # v4.15+
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Tested-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
index c9448e19847a3ef5eba44ffe1d813d37e3ba5e39..62290feddd5642ecee0daf76e6a5c731893c19cc 100644 (file)
--- a/arch/powerpc/include/asm/book3s/64/mmu.h
+++ b/arch/powerpc/include/asm/book3s/64/mmu.h
@@ -87,6 +87,9 @@ typedef struct {
        /* Number of bits in the mm_cpumask */
        atomic_t active_cpus;
 
+       /* Number of users of the external (Nest) MMU */
+       atomic_t copros;
+
        /* NPU NMMU context */
        struct npu_context *npu_context;
 

diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index e2a2b8400490049143edee40316313a906ca6db7..4f8a03c74e3f6d2b9c9f4fcb2cb1cfc50f4bd76d 100644 (file)
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -92,15 +92,23 @@ static inline void dec_mm_active_cpus(struct mm_struct *mm)
 static inline void mm_context_add_copro(struct mm_struct *mm)
 {
        /*
-        * On hash, should only be called once over the lifetime of
-        * the context, as we can't decrement the active cpus count
-        * and flush properly for the time being.
+        * If any copro is in use, increment the active CPU count
+        * in order to force TLB invalidations to be global as to
+        * propagate to the Nest MMU.
         */
-       inc_mm_active_cpus(mm);
+       if (atomic_inc_return(&mm->context.copros) == 1)
+               inc_mm_active_cpus(mm);
 }
 
 static inline void mm_context_remove_copro(struct mm_struct *mm)
 {
+       int c;
+
+       c = atomic_dec_if_positive(&mm->context.copros);
+
+       /* Detect imbalance between add and remove */
+       WARN_ON(c < 0);
+
        /*
         * Need to broadcast a global flush of the full mm before
         * decrementing active_cpus count, as the next TLBI may be
@@ -111,7 +119,7 @@ static inline void mm_context_remove_copro(struct mm_struct *mm)
         * for the time being. Invalidations will remain global if
         * used on hash.
         */
-       if (radix_enabled()) {
+       if (c == 0 && radix_enabled()) {
                flush_all_mm(mm);
                dec_mm_active_cpus(mm);
        }

diff --git a/arch/powerpc/mm/mmu_context_book3s64.c b/arch/powerpc/mm/mmu_context_book3s64.c
index 59c0766ae4e04d024cd33dad8faf577b7001c25c..5066276229f81b4bb5f738d045b9340e06a8d7e3 100644 (file)
--- a/arch/powerpc/mm/mmu_context_book3s64.c
+++ b/arch/powerpc/mm/mmu_context_book3s64.c
@@ -171,6 +171,7 @@ int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
        mm_iommu_init(mm);
 #endif
        atomic_set(&mm->context.active_cpus, 0);
+       atomic_set(&mm->context.copros, 0);
 
        return 0;
 }