[PATCH AUTOSEL 5.10 08/45] x86/hyperv: Fix kexec panic/hang issues

Sasha Levin
2021-01-20T03:54:20Z

From: Dexuan Cui <decui@microsoft.com>

[ Upstream commit dfe94d4086e40e92b1926bddcefa629b791e9b28 ]

Currently the kexec kernel can panic or hang due to 2 causes:

1) hv_cpu_die() is not called upon kexec, so the hypervisor corrupts the
old VP Assist Pages when the kexec kernel runs. The same issue is fixed
for hibernation in commit 421f090c819d ("x86/hyperv: Suspend/resume the
VP assist page for hibernation"). Now fix it for kexec.

2) hyperv_cleanup() is called too early. In the kexec path, the other CPUs
are stopped in hv_machine_shutdown() -> native_machine_shutdown(), so
between hv_kexec_handler() and native_machine_shutdown(), the other CPUs
can still try to access the hypercall page and cause panic. The workaround
"hv_hypercall_pg = NULL;" in hyperv_cleanup() is unreliabe. Move
hyperv_cleanup() to a better place.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20201222065541.24312-1-decui@microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/hyperv/hv_init.c | 4 ++++
arch/x86/include/asm/mshyperv.h | 2 ++
arch/x86/kernel/cpu/mshyperv.c | 18 ++++++++++++++++++
drivers/hv/vmbus_drv.c | 2 --
4 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index e04d90af4c27c..4638a52d8eaea 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -16,6 +16,7 @@
#include <asm/hyperv-tlfs.h>
#include <asm/mshyperv.h>
#include <asm/idtentry.h>
+#include <linux/kexec.h>
#include <linux/version.h>
#include <linux/vmalloc.h>
#include <linux/mm.h>
@@ -26,6 +27,8 @@
#include <linux/syscore_ops.h>
#include <clocksource/hyperv_timer.h>

+int hyperv_init_cpuhp;
+
void *hv_hypercall_pg;
EXPORT_SYMBOL_GPL(hv_hypercall_pg);

@@ -401,6 +404,7 @@ void __init hyperv_init(void)

register_syscore_ops(&hv_syscore_ops);

+ hyperv_init_cpuhp = cpuhp;
return;

remove_cpuhp_state:
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index ffc289992d1b0..30f76b9668579 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -74,6 +74,8 @@ static inline void hv_disable_stimer0_percpu_irq(int irq) {}

#if IS_ENABLED(CONFIG_HYPERV)
+extern int hyperv_init_cpuhp;
+
extern void *hv_hypercall_pg;
extern void __percpu **hyperv_pcpu_input_arg;

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 05ef1f4550cbd..6cc50ab07bded 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -135,14 +135,32 @@ static void hv_machine_shutdown(void)
{
if (kexec_in_progress && hv_kexec_handler)
hv_kexec_handler();
+
+ /*
+ * 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);
+
+ /* The function calls stop_other_cpus(). */
native_machine_shutdown();
+
+ /* Disable the hypercall page when there is only 1 active CPU. */
+ if (kexec_in_progress)
+ hyperv_cleanup();
}

static void hv_machine_crash_shutdown(struct pt_regs *regs)
{
if (hv_crash_handler)
hv_crash_handler(regs);
+
+ /* The function calls crash_smp_send_stop(). */
native_machine_crash_shutdown(regs);
+
+ /* Disable the hypercall page when there is only 1 active CPU. */
+ hyperv_cleanup();
}
#endif /* CONFIG_KEXEC_CORE */
#endif /* CONFIG_HYPERV */
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 4fad3e6745e53..a5a402e776c77 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -2542,7 +2542,6 @@ static void hv_kexec_handler(void)
/* Make sure conn_state is set as hv_synic_cleanup checks for it */
mb();
cpuhp_remove_state(hyperv_cpuhp_online);
- hyperv_cleanup();
};

static void hv_crash_handler(struct pt_regs *regs)
@@ -2558,7 +2557,6 @@ static void hv_crash_handler(struct pt_regs *regs)
cpu = smp_processor_id();
hv_stimer_cleanup(cpu);
hv_synic_disable_regs(cpu);
- hyperv_cleanup();
};

static int hv_synic_suspend(void)
--
2.27.0