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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/kallsyms.h> | |
| #define MODULE_NAME "zen_workaround" | |
| typedef int set_memory_fn_t(unsigned long, int); | |
| unsigned long need_symbol(const char *name) | |
| { | |
| unsigned long sym = kallsyms_lookup_name(name); | |
| if (sym) { | |
| pr_info("%s is 0x%lx\n", name, sym); | |
| } else { | |
| pr_err("could not find kernel symbol %s\n", name); | |
| } | |
| return sym; | |
| } | |
| static set_memory_fn_t *set_memory_ro, *set_memory_rw; | |
| static _Atomic u64 *x86_amd_ls_cfg_base_ptr; | |
| static _Atomic int *kernel_set_to_readonly_ptr; | |
| u64 set_speclockmap_disable(u64 msr) { | |
| return msr | BIT_64(54); | |
| } | |
| u64 unset_speclockmap_disable(u64 msr) { | |
| return msr & ~BIT_64(54); | |
| } | |
| 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) | |
| { | |
| u64 old_value = *x86_amd_ls_cfg_base_ptr; | |
| if (old_value) { | |
| int ret; | |
| u64 new_value = edit_msr(old_value); | |
| *kernel_set_to_readonly_ptr = 0; | |
| ret = set_memory_rw((unsigned long)x86_amd_ls_cfg_base_ptr, 1); | |
| *kernel_set_to_readonly_ptr = 1; | |
| if (ret) { | |
| pr_err("set_memory_rw failed with %d\n", ret); | |
| return -EPERM; | |
| } | |
| *x86_amd_ls_cfg_base_ptr = new_value; | |
| pr_info("x86_amd_ls_cfg_base was 0x%llx, setting to 0x%llx\n", old_value, new_value); | |
| *kernel_set_to_readonly_ptr = 0; | |
| ret = set_memory_ro((unsigned long)x86_amd_ls_cfg_base_ptr, 1); | |
| *kernel_set_to_readonly_ptr = 1; | |
| if (ret) { | |
| pr_err("set_memory_ro failed with %d\n", ret); | |
| // Not returning early because we still presumably set x86_amd_ls_cfg_base. | |
| } | |
| } else { | |
| pr_info("x86_amd_ls_cfg_base is unused."); | |
| } | |
| smp_call_function(edit_ls_cfg_on_cpu, edit_msr, 1); | |
| edit_ls_cfg_on_cpu(edit_msr); | |
| return 0; | |
| } | |
| static int __init zen_workaround_init(void) | |
| { | |
| if (!static_cpu_has(X86_FEATURE_ZEN)) { | |
| pr_err("Cannot use the Zen workaround on a non-Zen CPU\n"); | |
| return -EINVAL; | |
| } | |
| set_memory_ro = (set_memory_fn_t*) need_symbol("set_memory_ro"); | |
| set_memory_rw = (set_memory_fn_t*) need_symbol("set_memory_rw"); | |
| x86_amd_ls_cfg_base_ptr = (_Atomic u64*) need_symbol("x86_amd_ls_cfg_base"); | |
| kernel_set_to_readonly_ptr = (_Atomic int*) need_symbol("kernel_set_to_readonly"); | |
| if (!set_memory_ro || !set_memory_rw || !x86_amd_ls_cfg_base_ptr || | |
| !kernel_set_to_readonly_ptr) { | |
| return -ENOENT; | |
| } | |
| 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); | |
| } | |
| module_exit(zen_workaround_exit) | |
| MODULE_LICENSE("GPL"); |
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