KVM: SVM: Mark module parameters as __ro_after_init for security and performance

SVM module parameters such as avic, sev_enabled, npt_enabled, and
pause_filter_thresh are configured exclusively during initialization
(via kernel command line) and remain constant throughout runtime.
Additionally, sev_supported_vmsa_features and svm_gp_erratum_intercept,
while not exposed as module parameters, share the same initialization
pattern and runtime constancy.

Mark these variables with '__ro_after_init' to:
- Harden against accidental or malicious runtime modification
- Enable compiler and CPU optimizations (improved caching, branch prediction)
- Align with kernel security best practices for init-only configuration

The exception is 'iopm_base', which retains '__read_mostly' as it requires
updates during module unloading.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Link: https://patch.msgid.link/20260202095004.1765-1-lirongqing@baidu.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index f92214b1a9383bf8892ef9691dabc0a752699889..8c2bc98fed2b2e3ef89c07dc0d3d8c380e160256 100644 (file)
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -86,13 +86,13 @@ static const struct kernel_param_ops avic_ops = {
  * Enable / disable AVIC.  In "auto" mode (default behavior), AVIC is enabled
  * for Zen4+ CPUs with x2AVIC (and all other criteria for enablement are met).
  */
-static int avic = AVIC_AUTO_MODE;
+static int __ro_after_init avic = AVIC_AUTO_MODE;
 module_param_cb(avic, &avic_ops, &avic, 0444);
 __MODULE_PARM_TYPE(avic, "bool");
 
 module_param(enable_ipiv, bool, 0444);
 
-static bool force_avic;
+static bool __ro_after_init force_avic;
 module_param_unsafe(force_avic, bool, 0444);
 
 /* Note:

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 3f9c1aa39a0af5d9f1366d2a81ffd186f7db2b99..77ebc166abfd138adb6e34d39e6c882752a691c1 100644 (file)
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -52,18 +52,18 @@
 #define SNP_GUEST_VMM_ERR_GENERIC       (~0U)
 
 /* enable/disable SEV support */
-static bool sev_enabled = true;
+static bool __ro_after_init sev_enabled = true;
 module_param_named(sev, sev_enabled, bool, 0444);
 
 /* enable/disable SEV-ES support */
-static bool sev_es_enabled = true;
+static bool __ro_after_init sev_es_enabled = true;
 module_param_named(sev_es, sev_es_enabled, bool, 0444);
 
 /* enable/disable SEV-SNP support */
-static bool sev_snp_enabled = true;
+static bool __ro_after_init sev_snp_enabled = true;
 module_param_named(sev_snp, sev_snp_enabled, bool, 0444);
 
-static unsigned int nr_ciphertext_hiding_asids;
+static unsigned int __ro_after_init nr_ciphertext_hiding_asids;
 module_param_named(ciphertext_hiding_asids, nr_ciphertext_hiding_asids, uint, 0444);
 
 #define AP_RESET_HOLD_NONE             0

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 8f8bc863e214353284642830db5bd819ed594e5d..936f7652d1e49f70634d71928e468f523e2e3882 100644 (file)
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -110,52 +110,52 @@ static DEFINE_PER_CPU(u64, current_tsc_ratio);
  *     count only mode.
  */
 
-static unsigned short pause_filter_thresh = KVM_DEFAULT_PLE_GAP;
+static unsigned short __ro_after_init pause_filter_thresh = KVM_DEFAULT_PLE_GAP;
 module_param(pause_filter_thresh, ushort, 0444);
 
-static unsigned short pause_filter_count = KVM_SVM_DEFAULT_PLE_WINDOW;
+static unsigned short __ro_after_init pause_filter_count = KVM_SVM_DEFAULT_PLE_WINDOW;
 module_param(pause_filter_count, ushort, 0444);
 
 /* Default doubles per-vcpu window every exit. */
-static unsigned short pause_filter_count_grow = KVM_DEFAULT_PLE_WINDOW_GROW;
+static unsigned short __ro_after_init pause_filter_count_grow = KVM_DEFAULT_PLE_WINDOW_GROW;
 module_param(pause_filter_count_grow, ushort, 0444);
 
 /* Default resets per-vcpu window every exit to pause_filter_count. */
-static unsigned short pause_filter_count_shrink = KVM_DEFAULT_PLE_WINDOW_SHRINK;
+static unsigned short __ro_after_init pause_filter_count_shrink = KVM_DEFAULT_PLE_WINDOW_SHRINK;
 module_param(pause_filter_count_shrink, ushort, 0444);
 
 /* Default is to compute the maximum so we can never overflow. */
-static unsigned short pause_filter_count_max = KVM_SVM_DEFAULT_PLE_WINDOW_MAX;
+static unsigned short __ro_after_init pause_filter_count_max = KVM_SVM_DEFAULT_PLE_WINDOW_MAX;
 module_param(pause_filter_count_max, ushort, 0444);
 
 /*
  * Use nested page tables by default.  Note, NPT may get forced off by
  * svm_hardware_setup() if it's unsupported by hardware or the host kernel.
  */
-bool npt_enabled = true;
+bool __ro_after_init npt_enabled = true;
 module_param_named(npt, npt_enabled, bool, 0444);
 
 /* allow nested virtualization in KVM/SVM */
-static int nested = true;
+static int __ro_after_init nested = true;
 module_param(nested, int, 0444);
 
 /* enable/disable Next RIP Save */
-int nrips = true;
+int __ro_after_init nrips = true;
 module_param(nrips, int, 0444);
 
 /* enable/disable Virtual VMLOAD VMSAVE */
-static int vls = true;
+static int __ro_after_init vls = true;
 module_param(vls, int, 0444);
 
 /* enable/disable Virtual GIF */
-int vgif = true;
+int __ro_after_init vgif = true;
 module_param(vgif, int, 0444);
 
 /* enable/disable LBR virtualization */
-int lbrv = true;
+int __ro_after_init lbrv = true;
 module_param(lbrv, int, 0444);
 
-static int tsc_scaling = true;
+static int __ro_after_init tsc_scaling = true;
 module_param(tsc_scaling, int, 0444);
 
 module_param(enable_device_posted_irqs, bool, 0444);
@@ -164,19 +164,19 @@ bool __read_mostly dump_invalid_vmcb;
 module_param(dump_invalid_vmcb, bool, 0644);
 
 
-bool intercept_smi = true;
+bool __ro_after_init intercept_smi = true;
 module_param(intercept_smi, bool, 0444);
 
-bool vnmi = true;
+bool __ro_after_init vnmi = true;
 module_param(vnmi, bool, 0444);
 
 module_param(enable_mediated_pmu, bool, 0444);
 
-static bool svm_gp_erratum_intercept = true;
+static bool __ro_after_init svm_gp_erratum_intercept = true;
 
 static u8 rsm_ins_bytes[] = "\x0f\xaa";
 
-static unsigned long iopm_base;
+static unsigned long __read_mostly iopm_base;
 
 DEFINE_PER_CPU(struct svm_cpu_data, svm_data);