Thanks, Greg.
My first patch to the Linux kernel. Still making mistakes, but, learning through the documented process.
> -----Original Message-----
> From: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
> Sent: Wednesday, May 9, 2018 11:51 PM
> To: Sunil Muthuswamy <sunilmut@xxxxxxxxxxxxx>
> Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>;
> devel@xxxxxxxxxxxxxxxxxxxxxx; Stephen Hemminger
> <sthemmin@xxxxxxxxxxxxx>
> Subject: Re: [PATCH v1] Drivers: HV: Send one page worth of kmsg dump
> over Hyper-V during panic
>
> On Wed, May 09, 2018 at 07:19:24PM +0000, Sunil Muthuswamy wrote:
> > In the VM mode on Hyper-V, currently, when the kernel panics, an error
> > code and few register values are populated in an MSR and the Hypervisor
> > notified. This information is collected on the host. The amount of
> > information currently collected is found to be limited and not very
> > actionable. To gather more actionable data, such as stack trace, the
> > proposal is to write one page worth of kmsg data on an allocated page
> > and the Hypervisor notified of the page address through the MSR.
>
> Odd indentation, what editor made you do that? Please move it all to the
> left.
I inserted them. Will fix.
>
> >
> > CC: kys@xxxxxxxxxxxxx
> > CC: sthemmin@xxxxxxxxxxxxx
> > Signed-off-by: Sunil Muthuswamy <sunilmut@xxxxxxxxxxxxx>
> > ---
> > arch/x86/hyperv/hv_init.c | 28 +++++++++++++++++
> > arch/x86/include/asm/hyperv-tlfs.h | 5 ++--
> > arch/x86/include/asm/mshyperv.h | 1 +
> > drivers/hv/vmbus_drv.c | 61
> ++++++++++++++++++++++++++++++++++++++
> > 4 files changed, 93 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> > index cfecc22..88ee90d 100644
> > --- a/arch/x86/hyperv/hv_init.c
> > +++ b/arch/x86/hyperv/hv_init.c
> > @@ -395,6 +395,34 @@ void hyperv_report_panic(struct pt_regs *regs,
> > long err) } EXPORT_SYMBOL_GPL(hyperv_report_panic);
> >
> > +void hyperv_report_panic_msg(phys_addr_t pa, size_t size) {
> > + static bool panic_msg_reported;
> > +
> > + if (panic_msg_reported)
> > + return;
> > + panic_msg_reported = true;
>
> Why do you only care about the first message?
It is following the general direction from ' hyperv_report_panic', but, I don't think it needs to. Will change.
>
> > +
> > + /*
> > + * P3 to contain the physical address of the panic page & P4 to
> > + * contain the size of the panic data in that page. Rest of the
> > + * registers are no-op when the NOTIFY_MSG flag is set.
> > + */
> > + wrmsrl(HV_X64_MSR_CRASH_P0, 0);
> > + wrmsrl(HV_X64_MSR_CRASH_P1, 0);
> > + wrmsrl(HV_X64_MSR_CRASH_P2, 0);
> > + wrmsrl(HV_X64_MSR_CRASH_P3, pa);
> > + wrmsrl(HV_X64_MSR_CRASH_P4, size);
> > +
> > + /*
> > + * Let Hyper-V know there is crash data available along with
> > + * the panic message.
> > + */
> > + wrmsrl(HV_X64_MSR_CRASH_CTL,
> > + (HV_CRASH_CTL_CRASH_NOTIFY |
> HV_CRASH_CTL_CRASH_NOTIFY_MSG));
> > +} EXPORT_SYMBOL_GPL(hyperv_report_panic_msg);
> > +
> > bool hv_is_hyperv_initialized(void)
> > {
> > union hv_x64_msr_hypercall_contents hypercall_msr; diff --git
> > a/arch/x86/include/asm/hyperv-tlfs.h
> > b/arch/x86/include/asm/hyperv-tlfs.h
> > index 416cb0e..fc2932c 100644
> > --- a/arch/x86/include/asm/hyperv-tlfs.h
> > +++ b/arch/x86/include/asm/hyperv-tlfs.h
> > @@ -171,9 +171,10 @@
> > #define HV_X64_ENLIGHTENED_VMCS_RECOMMENDED (1 << 14)
> >
> > /*
> > - * Crash notification flag.
> > + * Crash notification flags.
> > */
> > -#define HV_CRASH_CTL_CRASH_NOTIFY (1ULL << 63)
> > +#define HV_CRASH_CTL_CRASH_NOTIFY (1ULL << 63)
> > +#define HV_CRASH_CTL_CRASH_NOTIFY_MSG (1ULL << 62)
>
> Not in numerical order?
>
> And can you use the BIT() macro here instead? Not a requirement, just a
> general question.
Will change in the next version.
>
> >
> > /* MSR used to identify the guest OS. */
> > #define HV_X64_MSR_GUEST_OS_ID 0x40000000
> > diff --git a/arch/x86/include/asm/mshyperv.h
> > b/arch/x86/include/asm/mshyperv.h index b90e796..ac83f2d 100644
> > --- a/arch/x86/include/asm/mshyperv.h
> > +++ b/arch/x86/include/asm/mshyperv.h
> > @@ -262,6 +262,7 @@ void hyperv_init(void); void
> > hyperv_setup_mmu_ops(void); void hyper_alloc_mmu(void); void
> > hyperv_report_panic(struct pt_regs *regs, long err);
> > +void hyperv_report_panic_msg(phys_addr_t pa, size_t size);
> > bool hv_is_hyperv_initialized(void);
> > void hyperv_cleanup(void);
> >
> > diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c index
> > b10fe26..40d915c 100644
> > --- a/drivers/hv/vmbus_drv.c
> > +++ b/drivers/hv/vmbus_drv.c
> > @@ -56,6 +56,8 @@ static struct completion probe_event;
> >
> > static int hyperv_cpuhp_online;
> >
> > +static void *hv_panic_page;
> > +
> > static int hyperv_panic_event(struct notifier_block *nb, unsigned long val,
> > void *args)
> > {
> > @@ -1018,6 +1020,41 @@ static void vmbus_isr(void)
> > add_interrupt_randomness(HYPERVISOR_CALLBACK_VECTOR, 0); }
> >
> > +/*
> > + * Callback from kmsg_dump. Grab as much as possible from the end of
> > +the kmsg
> > + * buffer and call into Hyper-V to transfer the data.
> > + */
> > +static void hv_kmsg_dump(struct kmsg_dumper *dumper,
> > + enum kmsg_dump_reason reason)
> > +{
> > + size_t bytes_written;
> > + phys_addr_t panic_pa;
> > +
> > + /* We are only interested in panics. */
> > + if (reason != KMSG_DUMP_PANIC)
> > + return;
> > +
> > + if (!hv_panic_page)
> > + return;
>
> How is this check every going to be possible? You don't register the dumper
> unless you have a page of memory, so no need to check this.
True, will fix.
>
> > +
> > + panic_pa = virt_to_phys(hv_panic_page);
> > +
> > + /*
> > + * Write dump contents to the page. No need to synchronize; panic
> should
> > + * be single-threaded.
> > + */
> > + if (!kmsg_dump_get_buffer(dumper, true, hv_panic_page,
> > + PAGE_SIZE, &bytes_written)) {
> > + pr_err("Hyper-V - Unable to get kmsg data for panic\n");
> > + return;
> > + }
> > +
> > + hyperv_report_panic_msg(panic_pa, bytes_written); }
> > +
> > +static struct kmsg_dumper hv_kmsg_dumper = {
> > + .dump = hv_kmsg_dump,
> > +};
> >
> > /*
> > * vmbus_bus_init -Main vmbus driver initialization routine.
> > @@ -1065,6 +1102,19 @@ static int vmbus_bus_init(void)
> > * Only register if the crash MSRs are available
> > */
> > if (ms_hyperv.misc_features &
> HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE)
> > {
> > + hv_panic_page = (void *)get_zeroed_page(GFP_KERNEL);
> > + if (!hv_panic_page) {
> > + ret = -ENOMEM;
> > + goto err_connect;
> > + }
> > +
> > + ret = kmsg_dump_register(&hv_kmsg_dumper);
> > + if (ret) {
> > + pr_err("Hyper-V - kmsg dump register failure
> 0x%x\n",
> > + ret);
> > + goto err_connect;
> > + }
> > +
> > register_die_notifier(&hyperv_die_block);
> > atomic_notifier_chain_register(&panic_notifier_list,
> > &hyperv_panic_block);
> > @@ -1081,6 +1131,10 @@ static int vmbus_bus_init(void)
> > hv_remove_vmbus_irq();
> >
> > bus_unregister(&hv_bus);
> > + if (hv_panic_page) {
> > + free_page((unsigned long)hv_panic_page);
>
> No need to check, free_page() can always be called with a 0 value
> successfully.
>
Will fix.
> > + hv_panic_page = NULL;
> > + }
> >
> > return ret;
> > }
> > @@ -1785,10 +1839,17 @@ static void __exit vmbus_exit(void)
> > vmbus_free_channels();
> >
> > if (ms_hyperv.misc_features &
> HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE)
> > {
> > + kmsg_dump_unregister(&hv_kmsg_dumper);
> > unregister_die_notifier(&hyperv_die_block);
> > atomic_notifier_chain_unregister(&panic_notifier_list,
> > &hyperv_panic_block);
> > }
> > +
> > + if (hv_panic_page) {
> > + free_page((unsigned long)hv_panic_page);
>
> Same here, no need to check.
Will fix.
>
> thanks,
>
> greg k-h
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