Hi Ben,

On 28/07/2025 10:49, Ben Horgan wrote:

On 7/11/25 19:36, James Morse wrote:

quoted

When a CPU comes online, it may bring a newly accessible MSC with
it. Only the default partid has its value reset by hardware, and
even then the MSC might not have been reset since its config was
previously dirtyied. e.g. Kexec.

Any in-use partid must have its configuration restored, or reset.
In-use partids may be held in caches and evicted later.

MSC are also reset when CPUs are taken offline to cover cases where
firmware doesn't reset the MSC over reboot using UEFI, or kexec
where there is no firmware involvement.

If the configuration for a RIS has not been touched since it was
brought online, it does not need resetting again.

To reset, write the maximum values for all discovered controls.

diff --git a/drivers/platform/arm64/mpam/mpam_devices.c b/drivers/platform/arm64/mpam/

mpam_devices.c
index 7b042a35405a..d014dbe0ab96 100644

--- a/drivers/platform/arm64/mpam/mpam_devices.c
+++ b/drivers/platform/arm64/mpam/mpam_devices.c

quoted

@@ -849,8 +850,116 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
      return 0;
  }
  +static void mpam_reset_msc_bitmap(struct mpam_msc *msc, u16 reg, u16 wd)
+{
+    u32 num_words, msb;
+    u32 bm = ~0;
+    int i;
+
+    lockdep_assert_held(&msc->part_sel_lock);
+
+    if (wd == 0)
+        return;
+
+    /*
+     * Write all ~0 to all but the last 32bit-word, which may
+     * have fewer bits...
+     */
+    num_words = DIV_ROUND_UP(wd, 32);
+    for (i = 0; i < num_words - 1; i++, reg += sizeof(bm))
+        __mpam_write_reg(msc, reg, bm);
+
+    /*
+     * ....and then the last (maybe) partial 32bit word. When wd is a
+     * multiple of 32, msb should be 31 to write a full 32bit word.
+     */
+    msb = (wd - 1) % 32;
+    bm = GENMASK(msb, 0);
+    if (bm)
+        __mpam_write_reg(msc, reg, bm);

Drop the 'if' as the 0 bit will always be part of the mask.

Yup, this was a harmless leftover of the versions that tried to optionally write the left over bits.

quoted

  @@ -1419,7 +1541,7 @@ static void mpam_enable_once(void)
      mpam_register_cpuhp_callbacks(mpam_cpu_online, mpam_cpu_offline);
        printk(KERN_INFO "MPAM enabled with %u partid and %u pmg\n",
-           mpam_partid_max + 1, mpam_pmg_max + 1);
+        READ_ONCE(mpam_partid_max) + 1, mpam_pmg_max + 1);

Belongs in 'arm_mpam: Probe MSCs to find the supported partid/pmg values'.

That value is now protected by a lock, and can't change at this point, so it no longer needs the READ_ONCE() anyway.


Thanks,

James