linux-kernel - Re: [RFC PATCH V3 01/11] x86/HV: Initialize GHCB page in Isolation VM

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Message-ID: <YMC2RSr/J1WYCvtz@8bytes.org>
Date:   Wed, 9 Jun 2021 14:38:29 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Tianyu Lan <ltykernel@...il.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, decui@...rosoft.com, tglx@...utronix.de,
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        hannes@...xchg.org, cai@....pw, krish.sadhukhan@...cle.com,
        saravanand@...com, Tianyu.Lan@...rosoft.com,
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Subject: Re: [RFC PATCH V3 01/11] x86/HV: Initialize GHCB page in Isolation VM

On Sun, May 30, 2021 at 11:06:18AM -0400, Tianyu Lan wrote:
> From: Tianyu Lan <Tianyu.Lan@...rosoft.com>
> 
> Hyper-V exposes GHCB page via SEV ES GHCB MSR for SNP guest
> to communicate with hypervisor. Map GHCB page for all
> cpus to read/write MSR register and submit hvcall request
> via GHCB.
> 
> Signed-off-by: Tianyu Lan <Tianyu.Lan@...rosoft.com>
> ---
>  arch/x86/hyperv/hv_init.c       | 60 ++++++++++++++++++++++++++++++---
>  arch/x86/include/asm/mshyperv.h |  2 ++
>  include/asm-generic/mshyperv.h  |  2 ++
>  3 files changed, 60 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index bb0ae4b5c00f..dc74d01cb859 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -60,6 +60,9 @@ static int hv_cpu_init(unsigned int cpu)
>  	struct hv_vp_assist_page **hvp = &hv_vp_assist_page[smp_processor_id()];
>  	void **input_arg;
>  	struct page *pg;
> +	u64 ghcb_gpa;
> +	void *ghcb_va;
> +	void **ghcb_base;

Any reason you can't reuse the SEV-ES support code in the Linux kernel?
It already has code to setup GHCBs for all vCPUs.

I see that you don't need #VC handling in your SNP VMs because of the
paravisor running underneath it, but just re-using the GHCB setup code
shouldn't be too hard.

Regards,

	Joerg