linux-kernel - Re: [PATCH] xen/pvhvm: add soft reset on kexec/kdump support

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Date:	Fri, 25 Sep 2015 09:59:37 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:	xen-devel@...ts.xenproject.org, x86@...nel.org,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xen/pvhvm: add soft reset on kexec/kdump support

On Fri, Sep 25, 2015 at 11:59:52AM +0200, Vitaly Kuznetsov wrote:
> Currently there is a number of issues preventing PVHVM Xen guests from
> doing successful kexec/kdump:
> - Bound event channels.
> - Registered vcpu_info.
> - PIRQ/emuirq mappings.
> - shared_info frame after XENMAPSPACE_shared_info operation.
> - Active grant mappings.
> Basically, newly booted kernel stumbles upon already set up Xen interfaces
> and there is no way to reestablish them. In Xen-4.7 a new feature called
> 'soft reset' is coming. A guest performing kexec/kdump operation is
> supposed to call SCHEDOP_shutdown hypercall with SHUTDOWN_soft_reset reason
> before jumping to new kernel. Hypervisor (with some help from toolstack)
> will do full domain cleanup (but keeping its memory and vCPU contexts
> intact) returning the guest to the state it had when it was first booted
> and thus allowing it to start over.
> 
> Doing SHUTDOWN_soft_reset on Xen hypervisors which don't support it is
> probably OK as by default all unknown shutdown reasons cause domain destroy
> with a message in toolstack log:
> 'Unknown shutdown reason code 5. Destroying domain.'
> which gives a clue to what the problem is and eliminates false
> expectations.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>

with s/pvhvm/hvm/

to match with the rest of the file.

Thanks.
> ---
>  arch/x86/xen/enlighten.c      | 23 +++++++++++++++++++++++
>  include/xen/interface/sched.h |  8 ++++++++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index 30d12af..e4be074 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -33,6 +33,10 @@
>  #include <linux/memblock.h>
>  #include <linux/edd.h>
>  
> +#ifdef CONFIG_KEXEC_CORE
> +#include <linux/kexec.h>
> +#endif
> +
>  #include <xen/xen.h>
>  #include <xen/events.h>
>  #include <xen/interface/xen.h>
> @@ -1807,6 +1811,21 @@ static struct notifier_block xen_hvm_cpu_notifier = {
>  	.notifier_call	= xen_hvm_cpu_notify,
>  };
>  
> +#ifdef CONFIG_KEXEC_CORE
> +static void xen_pvhvm_kexec_shutdown(void)
> +{
> +	native_machine_shutdown();
> +	if (kexec_in_progress)
> +		xen_reboot(SHUTDOWN_soft_reset);
> +}
> +
> +static void xen_pvhvm_crash_shutdown(struct pt_regs *regs)
> +{
> +	native_machine_crash_shutdown(regs);
> +	xen_reboot(SHUTDOWN_soft_reset);
> +}
> +#endif
> +
>  static void __init xen_hvm_guest_init(void)
>  {
>  	if (xen_pv_domain())
> @@ -1826,6 +1845,10 @@ static void __init xen_hvm_guest_init(void)
>  	x86_init.irqs.intr_init = xen_init_IRQ;
>  	xen_hvm_init_time_ops();
>  	xen_hvm_init_mmu_ops();
> +#ifdef CONFIG_KEXEC_CORE
> +	machine_ops.shutdown = xen_pvhvm_kexec_shutdown;
> +	machine_ops.crash_shutdown = xen_pvhvm_crash_shutdown;
> +#endif
>  }
>  #endif
>  
> diff --git a/include/xen/interface/sched.h b/include/xen/interface/sched.h
> index 9ce0839..f184909 100644
> --- a/include/xen/interface/sched.h
> +++ b/include/xen/interface/sched.h
> @@ -107,5 +107,13 @@ struct sched_watchdog {
>  #define SHUTDOWN_suspend    2  /* Clean up, save suspend info, kill.         */
>  #define SHUTDOWN_crash      3  /* Tell controller we've crashed.             */
>  #define SHUTDOWN_watchdog   4  /* Restart because watchdog time expired.     */
> +/*
> + * Domain asked to perform 'soft reset' for it. The expected behavior is to
> + * reset internal Xen state for the domain returning it to the point where it
> + * was created but leaving the domain's memory contents and vCPU contexts
> + * intact. This will allow the domain to start over and set up all Xen specific
> + * interfaces again.
> + */
> +#define SHUTDOWN_soft_reset 5
>  
>  #endif /* __XEN_PUBLIC_SCHED_H__ */
> -- 
> 2.4.3
> 
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