ACK: [focal:linux-azure][PATCH 1/1] x86/hyperv: Properly suspend/resume reenlightenment notifications

[Thadeu Lima de Souza Cascardo]

On Thu, Sep 17, 2020 at 11:04:57AM -0300, Marcelo Henrique Cerri wrote:
> From: Vitaly Kuznetsov <vkuznets at redhat.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1895980
> 
> Errors during hibernation with reenlightenment notifications enabled were
> reported:
> 
>  [   51.730435] PM: hibernation entry
>  [   51.737435] PM: Syncing filesystems ...
>  ...
>  [   54.102216] Disabling non-boot CPUs ...
>  [   54.106633] smpboot: CPU 1 is now offline
>  [   54.110006] unchecked MSR access error: WRMSR to 0x40000106 (tried to
>      write 0x47c72780000100ee) at rIP: 0xffffffff90062f24
>      native_write_msr+0x4/0x20)
>  [   54.110006] Call Trace:
>  [   54.110006]  hv_cpu_die+0xd9/0xf0
>  ...
> 
> Normally, hv_cpu_die() just reassigns reenlightenment notifications to some
> other CPU when the CPU receiving them goes offline. Upon hibernation, there
> is no other CPU which is still online so cpumask_any_but(cpu_online_mask)
> returns >= nr_cpu_ids and using it as hv_vp_index index is incorrect.
> Disable the feature when cpumask_any_but() fails.
> 
> Also, as we now disable reenlightenment notifications upon hibernation we
> need to restore them on resume. Check if hv_reenlightenment_cb was
> previously set and restore from hv_resume().
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets at redhat.com>
> Reviewed-by: Dexuan Cui <decui at microsoft.com>
> Reviewed-by: Tianyu Lan <Tianyu.Lan at microsoft.com>
> Link: https://lore.kernel.org/r/20200512160153.134467-1-vkuznets@redhat.com
> Signed-off-by: Wei Liu <wei.liu at kernel.org>
> (cherry picked from commit 38dce4195f0daefb566279fd9fd51e1fbd62ae1b)
> Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>
> ---
>  arch/x86/hyperv/hv_init.c | 19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index c14469fe93d2..1412e59eda01 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -226,10 +226,18 @@ static int hv_cpu_die(unsigned int cpu)
>  
>  	rdmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *((u64 *)&re_ctrl));
>  	if (re_ctrl.target_vp == hv_vp_index[cpu]) {
> -		/* Reassign to some other online CPU */
> +		/*
> +		 * Reassign reenlightenment notifications to some other online
> +		 * CPU or just disable the feature if there are no online CPUs
> +		 * left (happens on hibernation).
> +		 */
>  		new_cpu = cpumask_any_but(cpu_online_mask, cpu);
>  
> -		re_ctrl.target_vp = hv_vp_index[new_cpu];
> +		if (new_cpu < nr_cpu_ids)
> +			re_ctrl.target_vp = hv_vp_index[new_cpu];
> +		else
> +			re_ctrl.enabled = 0;
> +
>  		wrmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *((u64 *)&re_ctrl));
>  	}
>  
> @@ -293,6 +301,13 @@ static void hv_resume(void)
>  
>  	hv_hypercall_pg = hv_hypercall_pg_saved;
>  	hv_hypercall_pg_saved = NULL;
> +
> +	/*
> +	 * Reenlightenment notifications are disabled by hv_cpu_die(0),
> +	 * reenable them here if hv_reenlightenment_cb was previously set.
> +	 */
> +	if (hv_reenlightenment_cb)
> +		set_hv_tscchange_cb(hv_reenlightenment_cb);
>  }
>  
>  /* Note: when the ops are called, only CPU0 is online and IRQs are disabled. */
> -- 
> 2.25.1

Just a little concerned on testing for the second part of the commit, but as
it's restricted to the resume path and this is mentioned as work in progress,
please apply.

Acked-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>