KVM: Mark halt poll and other module parameters with appropriate memory attributes

Add '__read_mostly' to the halt polling parameters (halt_poll_ns,
halt_poll_ns_grow, halt_poll_ns_grow_start, halt_poll_ns_shrink) since
they are frequently read in hot paths (e.g., vCPU halt handling) but only
occasionally updated via sysfs. This improves cache locality on SMP
systems.

Conversely, mark 'allow_unsafe_mappings' and 'enable_virt_at_load' with
'__ro_after_init', as they are set only during module initialization via
kernel command line or early sysfs writes and remain constant thereafter.
This enhances security by preventing runtime modification and enables
compiler optimizations.

Signed-off-by: Li RongQing <lirongqing@baidu.com>
Link: https://patch.msgid.link/20260210062143.1739-1-lirongqing@baidu.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1bc1da66b4b02bab32e75ad6414b630e4d196af4..66371d8139d835d9a03b5455e895077eceaec622 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -76,22 +76,22 @@ MODULE_DESCRIPTION("Kernel-based Virtual Machine (KVM) Hypervisor");
 MODULE_LICENSE("GPL");
 
 /* Architectures should define their poll value according to the halt latency */
-unsigned int halt_poll_ns = KVM_HALT_POLL_NS_DEFAULT;
+unsigned int __read_mostly halt_poll_ns = KVM_HALT_POLL_NS_DEFAULT;
 module_param(halt_poll_ns, uint, 0644);
 EXPORT_SYMBOL_FOR_KVM_INTERNAL(halt_poll_ns);
 
 /* Default doubles per-vcpu halt_poll_ns. */
-unsigned int halt_poll_ns_grow = 2;
+unsigned int __read_mostly halt_poll_ns_grow = 2;
 module_param(halt_poll_ns_grow, uint, 0644);
 EXPORT_SYMBOL_FOR_KVM_INTERNAL(halt_poll_ns_grow);
 
 /* The start value to grow halt_poll_ns from */
-unsigned int halt_poll_ns_grow_start = 10000; /* 10us */
+unsigned int __read_mostly halt_poll_ns_grow_start = 10000; /* 10us */
 module_param(halt_poll_ns_grow_start, uint, 0644);
 EXPORT_SYMBOL_FOR_KVM_INTERNAL(halt_poll_ns_grow_start);
 
 /* Default halves per-vcpu halt_poll_ns. */
-unsigned int halt_poll_ns_shrink = 2;
+unsigned int __read_mostly halt_poll_ns_shrink = 2;
 module_param(halt_poll_ns_shrink, uint, 0644);
 EXPORT_SYMBOL_FOR_KVM_INTERNAL(halt_poll_ns_shrink);
 
@@ -99,7 +99,7 @@ EXPORT_SYMBOL_FOR_KVM_INTERNAL(halt_poll_ns_shrink);
  * Allow direct access (from KVM or the CPU) without MMU notifier protection
  * to unpinned pages.
  */
-static bool allow_unsafe_mappings;
+static bool __ro_after_init allow_unsafe_mappings;
 module_param(allow_unsafe_mappings, bool, 0444);
 
 /*
@@ -5574,7 +5574,7 @@ static struct miscdevice kvm_dev = {
 };
 
 #ifdef CONFIG_KVM_GENERIC_HARDWARE_ENABLING
-bool enable_virt_at_load = true;
+bool __ro_after_init enable_virt_at_load = true;
 module_param(enable_virt_at_load, bool, 0444);
 EXPORT_SYMBOL_FOR_KVM_INTERNAL(enable_virt_at_load);