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Linux kernel module for Zen workaround for rr
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| obj-m = zen_workaround.o | |
| all: | |
| make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules | |
| clean: | |
| make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean |
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| #include <linux/module.h> | |
| #include <linux/tracepoint.h> | |
| #define MODULE_NAME "zen_workaround" | |
| #define SPECLOCKMAP_DISABLE BIT_64(54) | |
| u64 set_speclockmap_disable(u64 msr) { | |
| return msr | SPECLOCKMAP_DISABLE; | |
| } | |
| u64 unset_speclockmap_disable(u64 msr) { | |
| return msr & ~SPECLOCKMAP_DISABLE; | |
| } | |
| typedef u64 (*edit_msr_func_t)(u64); | |
| static void edit_ls_cfg_on_cpu(void *info) | |
| { | |
| int cpu = get_cpu(); | |
| u64 value = 0; | |
| if (!rdmsrl_safe(MSR_AMD64_LS_CFG, &value)) { | |
| edit_msr_func_t edit_msr = (edit_msr_func_t) info; | |
| u64 new_value = edit_msr(value); | |
| if (!wrmsrl_safe(MSR_AMD64_LS_CFG, new_value)) { | |
| pr_info("MSR_AMD64_LS_CFG for cpu %d was 0x%llx, setting to 0x%llx\n", | |
| cpu, value, new_value); | |
| } else { | |
| pr_err("MSR_AMD64_LS_CFG for cpu %d was 0x%llx, setting to 0x%llx failed\n", | |
| cpu, value, new_value); | |
| } | |
| } | |
| } | |
| static int do_zen_workaround(edit_msr_func_t edit_msr) | |
| { | |
| smp_call_function(edit_ls_cfg_on_cpu, edit_msr, 1); | |
| edit_ls_cfg_on_cpu(edit_msr); | |
| return 0; | |
| } | |
| void on_write_msr(void *data, unsigned int msr, u64 val, int failed) { | |
| if (msr == MSR_AMD64_LS_CFG && !(val & SPECLOCKMAP_DISABLE)) { | |
| native_wrmsrl(MSR_AMD64_LS_CFG, set_speclockmap_disable(val)); | |
| } | |
| } | |
| static int __init zen_workaround_init(void) | |
| { | |
| int ret; | |
| if (!static_cpu_has(X86_FEATURE_ZEN)) { | |
| pr_err("Cannot use the Zen workaround on a non-Zen CPU\n"); | |
| return -EINVAL; | |
| } | |
| ret = tracepoint_probe_register(&__tracepoint_write_msr, on_write_msr, NULL); | |
| if (ret) { | |
| pr_err("Registering tracepoint probe failed\n"); | |
| return ret; | |
| } | |
| return do_zen_workaround(set_speclockmap_disable); | |
| } | |
| module_init(zen_workaround_init); | |
| static void __exit zen_workaround_exit(void) | |
| { | |
| do_zen_workaround(unset_speclockmap_disable); | |
| tracepoint_probe_unregister(&__tracepoint_write_msr, on_write_msr, NULL); | |
| } | |
| module_exit(zen_workaround_exit); | |
| MODULE_LICENSE("GPL"); |
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