linux-kernel - Re: [PATCH 01/13] x86/HV: Initialize GHCB page in Isolation VM

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Message-ID: <YQfctjRm16IP0qZy@8bytes.org>
Date:   Mon, 2 Aug 2021 13:53:26 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Tianyu Lan <ltykernel@...il.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
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Subject: Re: [PATCH 01/13] x86/HV: Initialize GHCB page in Isolation VM

On Wed, Jul 28, 2021 at 10:52:16AM -0400, Tianyu Lan wrote:
> +static int hyperv_init_ghcb(void)
> +{
> +	u64 ghcb_gpa;
> +	void *ghcb_va;
> +	void **ghcb_base;
> +
> +	if (!ms_hyperv.ghcb_base)
> +		return -EINVAL;
> +
> +	rdmsrl(MSR_AMD64_SEV_ES_GHCB, ghcb_gpa);
> +	ghcb_va = memremap(ghcb_gpa, HV_HYP_PAGE_SIZE, MEMREMAP_WB);

This deserves a comment. As I understand it, the GHCB pa is set by
Hyper-V or the paravisor, so the page does not need to be allocated by
Linux.
And it is not mapped unencrypted because the GHCB page is allocated
above the VTOM boundary?

> @@ -167,6 +190,31 @@ static int hv_cpu_die(unsigned int cpu)
>  {
>  	struct hv_reenlightenment_control re_ctrl;
>  	unsigned int new_cpu;
> +	unsigned long flags;
> +	void **input_arg;
> +	void *pg;
> +	void **ghcb_va = NULL;
> +
> +	local_irq_save(flags);
> +	input_arg = (void **)this_cpu_ptr(hyperv_pcpu_input_arg);
> +	pg = *input_arg;

Pg is never used later on, why is it set?