From 4ad79c874e53ebb7fe3b8ae7ac6c858a2121f415 Mon Sep 17 00:00:00 2001 From: Ben Horgan Date: Fri, 6 Mar 2026 18:27:16 +0000 Subject: arm_mpam: Fix null pointer dereference when restoring bandwidth counters When an MSC supporting memory bandwidth monitoring is brought offline and then online, mpam_restore_mbwu_state() calls __ris_msmon_read() via ipi to restore the configuration of the bandwidth counters. It doesn't care about the value read, mbwu_arg.val, and doesn't set it leading to a null pointer dereference when __ris_msmon_read() adds to it. This results in a kernel oops with a call trace such as: Call trace: __ris_msmon_read+0x19c/0x64c (P) mpam_restore_mbwu_state+0xa0/0xe8 smp_call_on_cpu_callback+0x1c/0x38 process_one_work+0x154/0x4b4 worker_thread+0x188/0x310 kthread+0x11c/0x130 ret_from_fork+0x10/0x20 Provide a local variable for val to avoid __ris_msmon_read() dereferencing a null pointer when adding to val. Fixes: 41e8a14950e1 ("arm_mpam: Track bandwidth counter state for power management") Signed-off-by: Ben Horgan Reviewed-by: James Morse Signed-off-by: James Morse Signed-off-by: Will Deacon --- drivers/resctrl/mpam_devices.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'drivers') diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c index 1eebc2602187..0666be6b0e88 100644 --- a/drivers/resctrl/mpam_devices.c +++ b/drivers/resctrl/mpam_devices.c @@ -1428,6 +1428,7 @@ static void mpam_reprogram_ris_partid(struct mpam_msc_ris *ris, u16 partid, static int mpam_restore_mbwu_state(void *_ris) { int i; + u64 val; struct mon_read mwbu_arg; struct mpam_msc_ris *ris = _ris; struct mpam_class *class = ris->vmsc->comp->class; @@ -1437,6 +1438,7 @@ static int mpam_restore_mbwu_state(void *_ris) mwbu_arg.ris = ris; mwbu_arg.ctx = &ris->mbwu_state[i].cfg; mwbu_arg.type = mpam_msmon_choose_counter(class); + mwbu_arg.val = &val; __ris_msmon_read(&mwbu_arg); } -- cgit v1.2.3 From c1376f1ff3f016a4b84e8030ed69df82e018d231 Mon Sep 17 00:00:00 2001 From: Ben Horgan Date: Fri, 6 Mar 2026 18:27:17 +0000 Subject: arm_mpam: Disable preemption when making accesses to fake MSC in kunit test Accesses to MSC must be made from a cpu that is affine to that MSC and the driver checks this in __mpam_write_reg() using smp_processor_id(). A fake in-memory MSC is used for testing. When using that, it doesn't matter which cpu we access it from but calling smp_processor_id() from a preemptible context gives warnings when running with CONFIG_DEBUG_PREEMPT. Add a test helper that wraps mpam_reset_msc_bitmap() with preemption disabled to ensure all (fake) MSC accesses are made with preemption disabled. Signed-off-by: Ben Horgan Reviewed-by: James Morse Signed-off-by: James Morse Signed-off-by: Will Deacon --- drivers/resctrl/test_mpam_devices.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) (limited to 'drivers') diff --git a/drivers/resctrl/test_mpam_devices.c b/drivers/resctrl/test_mpam_devices.c index 3e8d564a0c64..75bd41bcc395 100644 --- a/drivers/resctrl/test_mpam_devices.c +++ b/drivers/resctrl/test_mpam_devices.c @@ -322,6 +322,14 @@ static void test_mpam_enable_merge_features(struct kunit *test) mutex_unlock(&mpam_list_lock); } +static void __test_mpam_reset_msc_bitmap(struct mpam_msc *msc, u16 reg, u16 wd) +{ + /* Avoid warnings when running with CONFIG_DEBUG_PREEMPT */ + guard(preempt)(); + + mpam_reset_msc_bitmap(msc, reg, wd); +} + static void test_mpam_reset_msc_bitmap(struct kunit *test) { char __iomem *buf = kunit_kzalloc(test, SZ_16K, GFP_KERNEL); @@ -341,31 +349,31 @@ static void test_mpam_reset_msc_bitmap(struct kunit *test) test_result = (u32 *)(buf + MPAMCFG_CPBM); - mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 0); + __test_mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 0); KUNIT_EXPECT_EQ(test, test_result[0], 0); KUNIT_EXPECT_EQ(test, test_result[1], 0); test_result[0] = 0; test_result[1] = 0; - mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 1); + __test_mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 1); KUNIT_EXPECT_EQ(test, test_result[0], 1); KUNIT_EXPECT_EQ(test, test_result[1], 0); test_result[0] = 0; test_result[1] = 0; - mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 16); + __test_mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 16); KUNIT_EXPECT_EQ(test, test_result[0], 0xffff); KUNIT_EXPECT_EQ(test, test_result[1], 0); test_result[0] = 0; test_result[1] = 0; - mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 32); + __test_mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 32); KUNIT_EXPECT_EQ(test, test_result[0], 0xffffffff); KUNIT_EXPECT_EQ(test, test_result[1], 0); test_result[0] = 0; test_result[1] = 0; - mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 33); + __test_mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 33); KUNIT_EXPECT_EQ(test, test_result[0], 0xffffffff); KUNIT_EXPECT_EQ(test, test_result[1], 1); test_result[0] = 0; -- cgit v1.2.3 From fb75437b447875ae97ea3a173e734dbd553a3881 Mon Sep 17 00:00:00 2001 From: Krzysztof Kozlowski Date: Fri, 6 Mar 2026 18:27:18 +0000 Subject: arm_mpam: Force __iomem casts Code allocates standard kernel memory to pass to the MPAM, which expects __iomem. The code is safe, because __iomem accessors should work fine on kernel mapped memory, however leads to sparse warnings: test_mpam_devices.c:327:42: warning: incorrect type in initializer (different address spaces) test_mpam_devices.c:327:42: expected char [noderef] __iomem *buf test_mpam_devices.c:327:42: got void * test_mpam_devices.c:342:24: warning: cast removes address space '__iomem' of expression Cast the pointer to memory via __force to silence them. Signed-off-by: Krzysztof Kozlowski Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-kbuild-all/202512160133.eAzPdJv2-lkp@intel.com/ Acked-by: Ben Horgan Signed-off-by: James Morse Signed-off-by: Will Deacon --- drivers/resctrl/test_mpam_devices.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'drivers') diff --git a/drivers/resctrl/test_mpam_devices.c b/drivers/resctrl/test_mpam_devices.c index 75bd41bcc395..31871f519729 100644 --- a/drivers/resctrl/test_mpam_devices.c +++ b/drivers/resctrl/test_mpam_devices.c @@ -332,7 +332,7 @@ static void __test_mpam_reset_msc_bitmap(struct mpam_msc *msc, u16 reg, u16 wd) static void test_mpam_reset_msc_bitmap(struct kunit *test) { - char __iomem *buf = kunit_kzalloc(test, SZ_16K, GFP_KERNEL); + char __iomem *buf = (__force char __iomem *)kunit_kzalloc(test, SZ_16K, GFP_KERNEL); struct mpam_msc fake_msc = {}; u32 *test_result; @@ -347,7 +347,7 @@ static void test_mpam_reset_msc_bitmap(struct kunit *test) mutex_init(&fake_msc.part_sel_lock); mutex_lock(&fake_msc.part_sel_lock); - test_result = (u32 *)(buf + MPAMCFG_CPBM); + test_result = (__force u32 *)(buf + MPAMCFG_CPBM); __test_mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 0); KUNIT_EXPECT_EQ(test, test_result[0], 0); -- cgit v1.2.3