[Devel] (no subject)

[Konstantin Khorenko]

<20240828112158.3538342-1-anirudh at anirudhrb.com>
Subject: [PATCH RHEL9 COMMIT] ms/x86/hyperv: fix kexec crash due to VP assist page corruption

The commit is pushed to "branch-rh9-5.14.0-427.44.1.vz9.80.x-ovz" and will appear at git at bitbucket.org:openvz/vzkernel.git
after rh9-5.14.0-427.44.1.vz9.80.4
------>
commit b3bf7ee8e2ff76fee85455d48a5ea7581588577a
Author: Anirudh Rayabharam (Microsoft) <anirudh at anirudhrb.com>
Date:   Thu Jan 23 14:21:39 2025 +0800

    ms/x86/hyperv: fix kexec crash due to VP assist page corruption
    
    commit 9636be85cc5b ("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 dfe94d4086e4 ("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: stable at vger.kernel.org
    mFixes: 9636be85cc5b ("x86/hyperv: Fix hyperv_pcpu_input_arg handling when CPUs go online/offline")
    Signed-off-by: Anirudh Rayabharam (Microsoft) <anirudh at anirudhrb.com>
    Reviewed-by: Vitaly Kuznetsov <vkuznets at redhat.com>
    Reviewed-by: Michael Kelley <mhklinux at outlook.com>
    Link: https://lore.kernel.org/r/20240828112158.3538342-1-anirudh@anirudhrb.com
    Signed-off-by: Wei Liu <wei.liu at kernel.org>
    Message-ID: <20240828112158.3538342-1-anirudh at anirudhrb.com>
    
    Note: This patch resets VP assist page before kexec on old kernel, this
    means that kexec from the unfixed kernel to the fixed kernel will still
    be crashing.
    
    https://virtuozzo.atlassian.net/browse/VSTOR-97950
    (cherry picked from commit b9af6418279c4cf73ca073f8ea024992b38be8ab)
    
    Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
    
    Feature: fix ms/x86/hyperv
---
 arch/x86/hyperv/hv_init.c       | 5 +----
 arch/x86/include/asm/mshyperv.h | 1 -
 arch/x86/kernel/cpu/mshyperv.c  | 4 ++--
 3 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index ee199f802bfa..ecdfa0c485ee 100644
--- 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);
 
@@ -647,8 +646,6 @@ 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();
 
@@ -677,7 +674,7 @@ 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
index 896445edc6a8..ec95d6e9f168 100644
--- 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
index 2c889b0d2a08..abc8a7ab5c4e 100644
--- 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();