Known issue: arm64: allyesconfig: kvm: sys_regs.c:2654:17: error: ignoring return value of 'u64_replace_bits' New

Following build warnings / errors noticed with arm64 allyesconfig and build failed on the Linux next-20240711 tag.

Build error:s

arch/arm64/kvm/sys_regs.c: In function 'access_mdcr':
arch/arm64/kvm/sys_regs.c:2654:17: error: ignoring return value of 'u64_replace_bits' declared with attribute 'warn_unused_result' [-Werror=unused-result]
 2654 |                 u64_replace_bits(val, hpmn, MDCR_EL2_HPMN);

Arnd submitted a patch to fix this build regressions,

From: Arnd Bergmann <arnd@arndb.de>

u64_replace_bits() returns a modified word but does not actually modify
its argument, as pointed out by this new warning:

arch/arm64/kvm/sys_regs.c: In function 'access_mdcr':
arch/arm64/kvm/sys_regs.c:2654:17: error: ignoring return value of 'u64_replace_bits' declared with attribute 'warn_unused_result' [-Werror=unused-result]
 2654 |                 u64_replace_bits(val, hpmn, MDCR_EL2_HPMN);

The intention here must have been to update 'val', so do that instead.

Fixes: efff9dd2fee7 ("KVM: arm64: Handle out-of-bound write to MDCR_EL2.HPMN")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/arm64/kvm/sys_regs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 33aa4f5071b8..793fb19bebd6 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -2651,7 +2651,7 @@ static bool access_mdcr(struct kvm_vcpu *vcpu,
     */
    if (hpmn > vcpu->kvm->arch.nr_pmu_counters) {
        hpmn = vcpu->kvm->arch.nr_pmu_counters;
-       u64_replace_bits(val, hpmn, MDCR_EL2_HPMN);
+       val = u64_replace_bits(val, hpmn, MDCR_EL2_HPMN);
    }

    __vcpu_assign_sys_reg(vcpu, MDCR_EL2, val);
-- 
2.39.5