linux-kernel - Re: [PATCH v6 06/10] arm64: hyperv: Add kexec and panic handlers

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Message-ID: <86tv2pzdpr.wl-maz@kernel.org>
Date:   Sun, 15 Mar 2020 18:15:44 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     will@...nel.org, ardb@...nel.org, arnd@...db.de,
        catalin.marinas@....com, mark.rutland@....com,
        linux-arm-kernel@...ts.infradead.org, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
        linux-efi@...r.kernel.org, linux-arch@...r.kernel.org,
        olaf@...fle.de, apw@...onical.com, vkuznets@...hat.com,
        jasowang@...hat.com, marcelo.cerri@...onical.com,
        kys@...rosoft.com, sunilmut@...rosoft.com, boqun.feng@...il.com
Subject: Re: [PATCH v6 06/10] arm64: hyperv: Add kexec and panic handlers

On Sat, 14 Mar 2020 15:35:15 +0000,
Michael Kelley <mikelley@...rosoft.com> wrote:
> 
> Add functions to set up and remove kexec and panic
> handlers, and to inform Hyper-V about a guest panic.
> These functions are called from architecture independent
> code in the VMbus driver.
> 
> This code is built only when CONFIG_HYPERV is enabled.
> 
> Signed-off-by: Michael Kelley <mikelley@...rosoft.com>
> ---
>  arch/arm64/hyperv/hv_core.c  | 61 ++++++++++++++++++++++++++++++++++++++++++++
>  arch/arm64/hyperv/mshyperv.c | 26 +++++++++++++++++++
>  2 files changed, 87 insertions(+)
> 
> diff --git a/arch/arm64/hyperv/hv_core.c b/arch/arm64/hyperv/hv_core.c
> index 4aa6b8f..8d6de9f 100644
> --- a/arch/arm64/hyperv/hv_core.c
> +++ b/arch/arm64/hyperv/hv_core.c
> @@ -199,3 +199,64 @@ void hv_get_vpreg_128(u32 msr, struct hv_get_vp_register_output *res)
>  	kfree(output);
>  }
>  EXPORT_SYMBOL_GPL(hv_get_vpreg_128);
> +
> +void hyperv_report_panic(struct pt_regs *regs, long err)
> +{
> +	static bool panic_reported;
> +	u64 guest_id;
> +
> +	/*
> +	 * We prefer to report panic on 'die' chain as we have proper
> +	 * registers to report, but if we miss it (e.g. on BUG()) we need
> +	 * to report it on 'panic'.
> +	 */
> +	if (panic_reported)
> +		return;
> +	panic_reported = true;

How does this work when multiple vcpus are crashing at once? Are you
guaranteed to be single-threaded at this point?

> +
> +	guest_id = hv_get_vpreg(HV_REGISTER_GUEST_OSID);
> +
> +	/*
> +	 * Hyper-V provides the ability to store only 5 values.
> +	 * Pick the passed in error value, the guest_id, and the PC.
> +	 * The first two general registers are added arbitrarily.
> +	 */
> +	hv_set_vpreg(HV_REGISTER_CRASH_P0, err);
> +	hv_set_vpreg(HV_REGISTER_CRASH_P1, guest_id);
> +	hv_set_vpreg(HV_REGISTER_CRASH_P2, regs->pc);
> +	hv_set_vpreg(HV_REGISTER_CRASH_P3, regs->regs[0]);
> +	hv_set_vpreg(HV_REGISTER_CRASH_P4, regs->regs[1]);

How about reporting useful information, a pointer to some data
structure describing the fault? As it is, the usefulness of this is
pretty dubious.

> +
> +	/*
> +	 * Let Hyper-V know there is crash data available
> +	 */
> +	hv_set_vpreg(HV_REGISTER_CRASH_CTL, HV_CRASH_CTL_CRASH_NOTIFY);
> +}
> +EXPORT_SYMBOL_GPL(hyperv_report_panic);
> +
> +/*
> + * hyperv_report_panic_msg - report panic message to Hyper-V
> + * @pa: physical address of the panic page containing the message
> + * @size: size of the message in the page
> + */
> +void hyperv_report_panic_msg(phys_addr_t pa, size_t size)
> +{
> +	/*
> +	 * 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.
> +	 */
> +	hv_set_vpreg(HV_REGISTER_CRASH_P0, 0);
> +	hv_set_vpreg(HV_REGISTER_CRASH_P1, 0);
> +	hv_set_vpreg(HV_REGISTER_CRASH_P2, 0);
> +	hv_set_vpreg(HV_REGISTER_CRASH_P3, pa);
> +	hv_set_vpreg(HV_REGISTER_CRASH_P4, size);
> +
> +	/*
> +	 * Let Hyper-V know there is crash data available along with
> +	 * the panic message.
> +	 */
> +	hv_set_vpreg(HV_REGISTER_CRASH_CTL,
> +	       (HV_CRASH_CTL_CRASH_NOTIFY | HV_CRASH_CTL_CRASH_NOTIFY_MSG));
> +}
> +EXPORT_SYMBOL_GPL(hyperv_report_panic_msg);
> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> index ae6ece6..c58940d 100644
> --- a/arch/arm64/hyperv/mshyperv.c
> +++ b/arch/arm64/hyperv/mshyperv.c
> @@ -23,6 +23,8 @@
>  
>  static void (*vmbus_handler)(void);
>  static void (*hv_stimer0_handler)(void);
> +static void (*hv_kexec_handler)(void);
> +static void (*hv_crash_handler)(struct pt_regs *regs);

Why is this in the arch-specific code? Yes, it lives in the x86 arch
code too, but I don't see what prevents it from being moved to the
vmbus_drv.c code.

>  
>  static int vmbus_irq;
>  static long __percpu *vmbus_evt;
> @@ -137,3 +139,27 @@ void hv_remove_stimer0_irq(int irq)
>  	}
>  }
>  EXPORT_SYMBOL_GPL(hv_remove_stimer0_irq);
> +
> +void hv_setup_kexec_handler(void (*handler)(void))
> +{
> +	hv_kexec_handler = handler;
> +}
> +EXPORT_SYMBOL_GPL(hv_setup_kexec_handler);
> +
> +void hv_remove_kexec_handler(void)
> +{
> +	hv_kexec_handler = NULL;
> +}
> +EXPORT_SYMBOL_GPL(hv_remove_kexec_handler);
> +
> +void hv_setup_crash_handler(void (*handler)(struct pt_regs *regs))
> +{
> +	hv_crash_handler = handler;
> +}
> +EXPORT_SYMBOL_GPL(hv_setup_crash_handler);
> +
> +void hv_remove_crash_handler(void)
> +{
> +	hv_crash_handler = NULL;
> +}
> +EXPORT_SYMBOL_GPL(hv_remove_crash_handler);
> -- 
> 1.8.3.1
> 
> 

Thanks,

	M.

-- 
Jazz is not dead, it just smells funny.