Re: [RFC v2 3/7] arm64: cpufeature: handle conflicts based on capability

On 31/05/2019 15:00, Kristina Martsenko wrote:

On 30/05/2019 15:16, Suzuki K Poulose wrote:

quoted

On 05/29/2019 08:03 PM, Kristina Martsenko wrote:

quoted

Each system capability can be of either boot, local, or system scope,
depending on when the state of the capability is finalized. When we
detect a conflict on a late CPU, we either offline the CPU or panic the
system. We currently always panic if the conflict is caused by a boot
scope capability, and offline the CPU if the conflict is caused by a
local or system scope capability.

We're going to want to add new capability (for pointer authentication)
which needs to be boot scope but doesn't need to panic the system when a
conflict is detected. So add a new flag to specify whether the
capability requires the system to panic or not. Current boot scope
capabilities are updated to set the flag, so there should be no
functional change as a result of this patch.

Signed-off-by: Kristina Martsenko <redacted>

quoted

quoted

     @@ -249,6 +253,8 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
   #define ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU    ((u16)BIT(4))
   /* Is it safe for a late CPU to miss this capability when system has it */
   #define ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU    ((u16)BIT(5))
+/* Panic when a conflict is detected */
+#define ARM64_CPUCAP_PANIC_ON_CONFLICT        ((u16)BIT(6))
     /*
    * CPU errata workarounds that need to be enabled at boot time if one or

@@ -290,7 +296,8 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
    * CPU feature used early in the boot based on the boot CPU. All secondary
    * CPUs must match the state of the capability as detected by the boot CPU.
    */
-#define ARM64_CPUCAP_STRICT_BOOT_CPU_FEATURE ARM64_CPUCAP_SCOPE_BOOT_CPU
+#define ARM64_CPUCAP_STRICT_BOOT_CPU_FEATURE        \
+    (ARM64_CPUCAP_SCOPE_BOOT_CPU | ARM64_CPUCAP_PANIC_ON_CONFLICT)

You may want to update the comment to mention that a conflict triggers
kernel panic, as it is more within the control of the "cap" behavior.

Do you mean to update the comment above ARM64_CPUCAP_STRICT_BOOT_CPU_FEATURE?
To something like the following?

/*
  * CPU feature used early in the boot based on the boot CPU. All secondary
  * CPUs must match the state of the capability as detected by the boot CPU. In
  * case of a conflict, a kernel panic is triggered.
  */

Yes. That looks good.
Earlier it was upto the caller to decide when there was a conflict with
Boot features to take an action. But with this change we Panic for STRICT_BOOT
features.

Suzuki

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