From: Paul Burton <paul.burton@xxxxxxxxxx> [ Upstream commit fa7a3b4a7217b40bf58c4f38e5ee573b43a8aa2f ] On pre-r6 systems with the MT ASE the CPS SMP code included checks to halt the VPE running mips_cps_boot_vpes() if its bit in the struct core_boot_config vpe_mask field is clear. This was largely done in order to allow us to start arbitrary VPEs within a core despite the fact that hardware is typically configured to run only VPE0 after powering up a core. VPE0 would start the desired other VPEs, halt itself, and the fact that VPE0 started would be largely hidden & irrelevant. In MIPSr6 multithreading we have control over which VPs start executing when a core powers up via the cores CPC registers accessed remotely through the redirect block. For this reason the MIPSr6 multithreading path in mips_cps_boot_vpes() hasn't bothered up until now to handle halting the VP running it. However it is possible to power up cores entirely in hardware by using a pwr_up pin associated with the core. Unfortunately some systems wire this pin to a logic 1, which means that it is possible for a core to power up at a point that software doesn't expect. The result is that we generally go execute the kernel on a CPU that ought not to be running & the results can be unpredictable. Handle this case by stopping VPs that we don't expect to be running in mips_cps_boot_vpes() - with this change even if a core powers up it will do nothing useful & all VPs within it will stop running before they proceed to run general kernel code & do any damage. Ideally we would produce some sort of warning here, but given the stage of core bringup this happens at that would be non-trivial. We also will only hit this if a core starts up after being offlined via hotplug, and when that happens we will already produce a warning that the CPU didn't power down in cps_cpu_die() which seems sufficient. Signed-off-by: Paul Burton <paul.burton@xxxxxxxxxx> Cc: linux-mips@xxxxxxxxxxxxxx Patchwork: https://patchwork.linux-mips.org/patch/16198/ Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx> --- arch/mips/kernel/cps-vec.S | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/mips/kernel/cps-vec.S b/arch/mips/kernel/cps-vec.S index a00e87b0256d..b849fe6aad94 100644 --- a/arch/mips/kernel/cps-vec.S +++ b/arch/mips/kernel/cps-vec.S @@ -22,6 +22,7 @@ #define GCR_CL_COHERENCE_OFS 0x2008 #define GCR_CL_ID_OFS 0x2028 +#define CPC_CL_VC_STOP_OFS 0x2020 #define CPC_CL_VC_RUN_OFS 0x2028 .extern mips_cm_base @@ -376,8 +377,12 @@ LEAF(mips_cps_boot_vpes) PTR_LI t2, UNCAC_BASE PTR_ADD t1, t1, t2 - /* Set VC_RUN to the VPE mask */ + /* Start any other VPs that ought to be running */ PTR_S ta2, CPC_CL_VC_RUN_OFS(t1) + + /* Ensure this VP stops running if it shouldn't be */ + not ta2 + PTR_S ta2, CPC_CL_VC_STOP_OFS(t1) ehb #elif defined(CONFIG_MIPS_MT) -- 2.15.1
