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

[Tom Lendacky]

On 5/1/23 03:57, Tianyu Lan wrote:
> From: Tianyu Lan <tiala@xxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxx>
> ---
>   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);
>   	}