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Subject: RE: [PATCH v4] hyperv: root partition faults writing to VP ASSIST MSR
 PAGE
Thread-Topic: [PATCH v4] hyperv: root partition faults writing to VP ASSIST
 MSR PAGE
Thread-Index: AQHXhWXjNWmxIS5YjUS2UQiuiH/FdKtcNdJw
Date:   Sat, 31 Jul 2021 00:12:45 +0000
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References: <20210730171056.2820-1-kumarpraveen@linux.microsoft.com>
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>  	hv_common_cpu_die(cpu);
>=20
> -	if (hv_vp_assist_page && hv_vp_assist_page[cpu])
> -		wrmsrl(HV_X64_MSR_VP_ASSIST_PAGE, 0);
> +	if (hv_vp_assist_page && hv_vp_assist_page[cpu]) {
> +		union hv_vp_assist_msr_contents msr =3D {0};
> +		if (hv_root_partition) {
> +			/*
> +			 * For Root partition the VP ASSIST page is mapped to
> +			 * hypervisor provided page, and thus, we unmap the
> +			 * page here and nullify it, so that in future we have
> +			 * correct page address mapped in hv_cpu_init.
> +			 */
> +			memunmap(hv_vp_assist_page[cpu]);
> +			hv_vp_assist_page[cpu] =3D NULL;
> +			rdmsrl(HV_X64_MSR_VP_ASSIST_PAGE, msr.as_uint64);

If the vp assist page was previously enabled for root, it will continue to =
stay enabled
when you 'wrmsr' below. We need to explicitly set the enable bit to 0.

> +		}
> +		wrmsrl(HV_X64_MSR_VP_ASSIST_PAGE, msr.as_uint64);
> +	}