x86/hyperv: fix kexec crash due to VP assist page corruption

commit 9636be8 ("x86/hyperv: Fix hyperv_pcpu_input_arg handling when CPUs go online/offline") introduces a new cpuhp state for hyperv initialization. cpuhp_setup_state() returns the state number if state is CPUHP_AP_ONLINE_DYN or CPUHP_BP_PREPARE_DYN and 0 for all other states. For the hyperv case, since a new cpuhp state was introduced it would return 0. However, in hv_machine_shutdown(), the cpuhp_remove_state() call is conditioned upon "hyperv_init_cpuhp > 0". This will never be true and so hv_cpu_die() won't be called on all CPUs. This means the VP assist page won't be reset. When the kexec kernel tries to setup the VP assist page again, the hypervisor corrupts the memory region of the old VP assist page causing a panic in case the kexec kernel is using that memory elsewhere. This was originally fixed in commit dfe94d4 ("x86/hyperv: Fix kexec panic/hang issues"). Get rid of hyperv_init_cpuhp entirely since we are no longer using a dynamic cpuhp state and use CPUHP_AP_HYPERV_ONLINE directly with cpuhp_remove_state(). Cc: [email protected] Fixes: 9636be8 ("x86/hyperv: Fix hyperv_pcpu_input_arg handling when CPUs go online/offline") Signed-off-by: Anirudh Rayabharam (Microsoft) <[email protected]> Reviewed-by: Vitaly Kuznetsov <[email protected]> Reviewed-by: Michael Kelley <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Wei Liu <[email protected]> Message-ID: <[email protected]>
sedwards · Sep 5, 2024 · b9af641 · b9af641
1 parent 4430556
commit b9af641
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Showing 3 changed files with 3 additions and 7 deletions.
diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
@@ -35,7 +35,6 @@
 #include <clocksource/hyperv_timer.h>
 #include <linux/highmem.h>
 
-int hyperv_init_cpuhp;
 u64 hv_current_partition_id = ~0ull;
 EXPORT_SYMBOL_GPL(hv_current_partition_id);
 
@@ -607,8 +606,6 @@ void __init hyperv_init(void)
 
 	register_syscore_ops(&hv_syscore_ops);
 
-	hyperv_init_cpuhp = cpuhp;
-
 	if (cpuid_ebx(HYPERV_CPUID_FEATURES) & HV_ACCESS_PARTITION_ID)
 		hv_get_partition_id();
 
@@ -637,7 +634,7 @@ void __init hyperv_init(void)
 clean_guest_os_id:
 	wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
 	hv_ivm_msr_write(HV_X64_MSR_GUEST_OS_ID, 0);
-	cpuhp_remove_state(cpuhp);
+	cpuhp_remove_state(CPUHP_AP_HYPERV_ONLINE);
 free_ghcb_page:
 	free_percpu(hv_ghcb_pg);
 free_vp_assist_page:

diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
@@ -40,7 +40,6 @@ static inline unsigned char hv_get_nmi_reason(void)
 }
 
 #if IS_ENABLED(CONFIG_HYPERV)
-extern int hyperv_init_cpuhp;
 extern bool hyperv_paravisor_present;
 
 extern void *hv_hypercall_pg;

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
@@ -199,8 +199,8 @@ static void hv_machine_shutdown(void)
 	 * Call hv_cpu_die() on all the CPUs, otherwise later the hypervisor
 	 * corrupts the old VP Assist Pages and can crash the kexec kernel.
 	 */
-	if (kexec_in_progress && hyperv_init_cpuhp > 0)
-		cpuhp_remove_state(hyperv_init_cpuhp);
+	if (kexec_in_progress)
+		cpuhp_remove_state(CPUHP_AP_HYPERV_ONLINE);
 
 	/* The function calls stop_other_cpus(). */
 	native_machine_shutdown();