linux-kernel - Re: [RFC PATCH V5 02/15] x86/hyperv: Decrypt hv vp assist page in sev-snp enlightened guest

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Date:   Mon, 1 May 2023 10:10:33 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Tianyu Lan <ltykernel@...il.com>, luto@...nel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        seanjc@...gle.com, pbonzini@...hat.com, jgross@...e.com,
        tiala@...rosoft.com, kirill@...temov.name,
        jiangshan.ljs@...group.com, peterz@...radead.org,
        ashish.kalra@....com, srutherford@...gle.com,
        akpm@...ux-foundation.org, anshuman.khandual@....com,
        pawan.kumar.gupta@...ux.intel.com, adrian.hunter@...el.com,
        daniel.sneddon@...ux.intel.com, alexander.shishkin@...ux.intel.com,
        sandipan.das@....com, ray.huang@....com, brijesh.singh@....com,
        michael.roth@....com, venu.busireddy@...cle.com,
        sterritt@...gle.com, tony.luck@...el.com, samitolvanen@...gle.com,
        fenghua.yu@...el.com
Cc:     pangupta@....com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-hyperv@...r.kernel.org,
        linux-arch@...r.kernel.org
Subject: Re: [RFC PATCH V5 02/15] x86/hyperv: Decrypt hv vp assist page in
 sev-snp enlightened guest

On 5/1/23 03:57, Tianyu Lan wrote:
> From: Tianyu Lan <tiala@...rosoft.com>
> 
> hv vp assist page is shared between sev snp guest and hyperv. Decrypt
> the page when use it.

You aren't actually decrypting the page, you're changing the mapping from 
private/encrypted to shared/unencrypted (hence the memset that follows to 
clear the page to zeroes).

And please capitalize where necessary, e.g., SEV-SNP, Hyper-V, etc.

Thanks,
Tom

> 
> Signed-off-by: Tianyu Lan <tiala@...rosoft.com>
> ---
>   arch/x86/hyperv/hv_init.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index a5f9474f08e1..9f3e2d71d015 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -18,6 +18,7 @@
>   #include <asm/hyperv-tlfs.h>
>   #include <asm/mshyperv.h>
>   #include <asm/idtentry.h>
> +#include <asm/set_memory.h>
>   #include <linux/kexec.h>
>   #include <linux/version.h>
>   #include <linux/vmalloc.h>
> @@ -113,6 +114,11 @@ static int hv_cpu_init(unsigned int cpu)
>   
>   	}
>   	if (!WARN_ON(!(*hvp))) {
> +		if (hv_isolation_type_en_snp()) {
> +			WARN_ON_ONCE(set_memory_decrypted((unsigned long)(*hvp), 1));
> +			memset(*hvp, 0, PAGE_SIZE);
> +		}
> +
>   		msr.enable = 1;
>   		wrmsrl(HV_X64_MSR_VP_ASSIST_PAGE, msr.as_uint64);
>   	}