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Subject: Re: [PATCH] x86/hyperv: Properly suspend/resume reenlightenment
 notifications
To:     Vitaly Kuznetsov <vkuznets@redhat.com>,
        linux-hyperv@vger.kernel.org
Cc:     Wei Liu <wei.liu@kernel.org>, x86@kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        Michael Kelley <mikelley@microsoft.com>,
        Dexuan Cui <decui@microsoft.com>,
        Tianyu Lan <Tianyu.Lan@microsoft.com>
References: <20200512160153.134467-1-vkuznets@redhat.com>
From:   Tianyu Lan <ltykernel@gmail.com>
Message-ID: <3507d1b3-8d90-8d0e-c20f-a75f9f280230@gmail.com>
Date:   Wed, 13 May 2020 21:35:26 +0800
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On 5/13/2020 12:01 AM, Vitaly Kuznetsov wrote:
> 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@redhat.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 fd51bac11b46..acf76b466db6 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. */
> 

Reviewed-by: Tianyu Lan <Tianyu.Lan@microsoft.com>