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Date:   Tue, 22 Feb 2022 10:55:41 +0000
From:   Wei Liu <wei.liu@kernel.org>
To:     Tianyu Lan <ltykernel@gmail.com>
Cc:     kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com,
        wei.liu@kernel.org, decui@microsoft.com, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        x86@kernel.org, hpa@zytor.com, brijesh.singh@amd.com,
        michael.roth@amd.com, jroedel@suse.de, Tianyu.Lan@microsoft.com,
        thomas.lendacky@amd.com, michael.h.kelley@microsoft.com,
        linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC FATCH] x86/Hyper-V: Add SEV negotiate protocol support in
 Isolation VM.
Message-ID: <20220222105541.izv4psjychjx5ooq@liuwe-devbox-debian-v2>
References: <20220207160928.111718-1-ltykernel@gmail.com>
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On Mon, Feb 07, 2022 at 11:09:28AM -0500, Tianyu Lan wrote:
> From: Tianyu Lan <Tianyu.Lan@microsoft.com>
> 
> Hyper-V Isolation VM code uses sev_es_ghcb_hv_call() to read/write MSR
> via ghcb page. The SEV-ES guest should call the sev_es_negotiate_protocol()
> to negotiate the GHCB protocol version before establishing the GHCB. Call
> sev_es_negotiate_protocol() in the hyperv_init_ghcb().
> 
> Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
> ---
> This patch based on the "Add AMD Secure Nested Paging (SEV-SNP) Guest Support"
> patchset. https://lore.kernel.org/lkml/20220128171804.569796-1-brijesh.singh@amd.com/
> 
>  arch/x86/hyperv/hv_init.c    | 6 ++++++
>  arch/x86/include/asm/sev.h   | 2 ++
>  arch/x86/kernel/sev-shared.c | 2 +-
>  arch/x86/kernel/sev.c        | 4 ++--
>  4 files changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index 24f4a06ac46a..a22303fccf02 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -28,6 +28,7 @@
>  #include <linux/syscore_ops.h>
>  #include <clocksource/hyperv_timer.h>
>  #include <linux/highmem.h>
> +#include <asm/sev.h>
>  
>  int hyperv_init_cpuhp;
>  u64 hv_current_partition_id = ~0ull;
> @@ -69,6 +70,11 @@ static int hyperv_init_ghcb(void)
>  	ghcb_base = (void **)this_cpu_ptr(hv_ghcb_pg);
>  	*ghcb_base = ghcb_va;
>  
> +	sev_es_negotiate_protocol();

The return value should be checked, right?

There is no logical connection between this function call and the wrmsrl
below. Is there new information available after calling
sev_es_negotiate_protocol?

> +
> +	/* Write ghcb page back after negotiating protocol. */
> +	wrmsrl(MSR_AMD64_SEV_ES_GHCB, ghcb_gpa);
> +	VMGEXIT();
>  	return 0;
>  }
>  
[...]
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index 3568b3303314..46c53c4885ee 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -167,12 +167,12 @@ void noinstr __sev_es_ist_exit(void)
>  	this_cpu_write(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC], *(unsigned long *)ist);
>  }
>  
> -static inline u64 sev_es_rd_ghcb_msr(void)
> +inline u64 sev_es_rd_ghcb_msr(void)
>  {
>  	return __rdmsr(MSR_AMD64_SEV_ES_GHCB);
>  }
>  
> -static __always_inline void sev_es_wr_ghcb_msr(u64 val)
> +__always_inline void sev_es_wr_ghcb_msr(u64 val)

Why are these needed? They are not used anywhere in this patch.

Thanks,
Wei.

>  {
>  	u32 low, high;
>  
> -- 
> 2.25.1
>