prefetch_disable_bits is set by rdtgroup_locksetup_enter() from a
value provided by the architecture, but is largely read by other
architecture helpers.

Instead of exporting this value, make
resctrl_arch_get_prefetch_disable_bits() set it so that the other
arch-code helpers can use the cached-value.

Signed-off-by: James Morse <james.morse@arm.com>
Tested-by: Carl Worth <carl@os.amperecomputing.com> # arm64
Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
---
 arch/x86/kernel/cpu/resctrl/pseudo_lock.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
index 56e59441d6ae..0fee49fc153a 100644
--- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
+++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
@@ -84,6 +84,8 @@ static const struct class pseudo_lock_class = {
  */
 u64 resctrl_arch_get_prefetch_disable_bits(void)
 {
+	prefetch_disable_bits = 0;
+
 	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL ||
 	    boot_cpu_data.x86 != 6)
 		return 0;
@@ -99,7 +101,8 @@ u64 resctrl_arch_get_prefetch_disable_bits(void)
 		 * 3    DCU IP Prefetcher Disable (R/W)
 		 * 63:4 Reserved
 		 */
-		return 0xF;
+		prefetch_disable_bits = 0xF;
+		break;
 	case INTEL_ATOM_GOLDMONT:
 	case INTEL_ATOM_GOLDMONT_PLUS:
 		/*
@@ -110,10 +113,11 @@ u64 resctrl_arch_get_prefetch_disable_bits(void)
 		 * 2     DCU Hardware Prefetcher Disable (R/W)
 		 * 63:3  Reserved
 		 */
-		return 0x5;
+		prefetch_disable_bits = 0x5;
+		break;
 	}
 
-	return 0;
+	return prefetch_disable_bits;
 }
 
 /**
@@ -713,8 +717,7 @@ int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp)
 	 * Not knowing the bits to disable prefetching implies that this
 	 * platform does not support Cache Pseudo-Locking.
 	 */
-	prefetch_disable_bits = resctrl_arch_get_prefetch_disable_bits();
-	if (prefetch_disable_bits == 0) {
+	if (resctrl_arch_get_prefetch_disable_bits() == 0) {
 		rdt_last_cmd_puts("Pseudo-locking not supported\n");
 		return -EINVAL;
 	}
-- 
2.39.2

Hi James,

On 10/4/24 11:03 AM, James Morse wrote:
> prefetch_disable_bits is set by rdtgroup_locksetup_enter() from a
> value provided by the architecture, but is largely read by other
> architecture helpers.
> 
> Instead of exporting this value, make
> resctrl_arch_get_prefetch_disable_bits() set it so that the other
> arch-code helpers can use the cached-value.

The "exporting" term has already caused some confusion. How about:

Make resctrl_arch_get_prefetch_disable_bits() set prefetch_disable_bits
so that it can be isolated to arch-code from where the other arch-code
helpers can use its cached-value.

(Please feel free to improve.)

Reinette