The v2 patch that I sent was prior to responding to this thread. I am sending out v3 which addresses the comments here.
> -----Original Message-----
> From: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
> Sent: Saturday, May 19, 2018 12:01 AM
> To: Sunil Muthuswamy <sunilmut@xxxxxxxxxxxxx>
> Cc: devel@xxxxxxxxxxxxxxxxxxxxxx; Haiyang Zhang
> <haiyangz@xxxxxxxxxxxxx>; Stephen Hemminger
> <sthemmin@xxxxxxxxxxxxx>
> Subject: Re: [PATCH v1] Drivers: HV: Send one page worth of kmsg dump
> over Hyper-V during panic
>
> On Fri, May 18, 2018 at 09:00:51PM +0000, Sunil Muthuswamy wrote:
> > 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.
>
> You didn't do that :(
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