Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Vitaly Kuznetsov <vkuznets@redhat.com>
To:     Tianyu Lan <ltykernel@gmail.com>, kys@microsoft.com,
        haiyangz@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,
        daniel.lezcano@linaro.org, arnd@arndb.de,
        michael.h.kelley@microsoft.com
Cc:     Tianyu Lan <tiala@microsoft.com>, linux-arch@vger.kernel.org,
        linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5/9] x86/hyperv: Use vmmcall to implement Hyper-V
 hypercall in sev-snp enlightened guest
In-Reply-To: <20230601151624.1757616-6-ltykernel@gmail.com>
References: <20230601151624.1757616-1-ltykernel@gmail.com>
 <20230601151624.1757616-6-ltykernel@gmail.com>
Date:   Mon, 05 Jun 2023 15:00:33 +0200
Message-ID: <87wn0ijc7i.fsf@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Tianyu Lan <ltykernel@gmail.com> writes:

> From: Tianyu Lan <tiala@microsoft.com>
>
> In sev-snp enlightened guest, Hyper-V hypercall needs
> to use vmmcall to trigger vmexit and notify hypervisor
> to handle hypercall request.
>
> There is no x86 SEV SNP feature flag support so far and
> hardware provides MSR_AMD64_SEV register to check SEV-SNP
> capability with MSR_AMD64_SEV_ENABLED bit. ALTERNATIVE can't
> work without SEV-SNP x86 feature flag. May add later when
> the associated flag is introduced. 
>
> Signed-off-by: Tianyu Lan <tiala@microsoft.com>
> ---
>  arch/x86/include/asm/mshyperv.h | 44 ++++++++++++++++++++++++---------
>  1 file changed, 33 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 31c476f4e656..d859d7c5f5e8 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -61,16 +61,25 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
>  	u64 hv_status;
>  
>  #ifdef CONFIG_X86_64
> -	if (!hv_hypercall_pg)
> -		return U64_MAX;
> +	if (hv_isolation_type_en_snp()) {

Would it be possible to redo 'hv_isolation_type_en_snp()' into a static
inline doing static_branch_unlikely() so we avoid function call penalty
here?

> +		__asm__ __volatile__("mov %4, %%r8\n"
> +				     "vmmcall"
> +				     : "=a" (hv_status), ASM_CALL_CONSTRAINT,
> +				       "+c" (control), "+d" (input_address)
> +				     :  "r" (output_address)
> +				     : "cc", "memory", "r8", "r9", "r10", "r11");
> +	} else {
> +		if (!hv_hypercall_pg)
> +			return U64_MAX;
>  
> -	__asm__ __volatile__("mov %4, %%r8\n"
> -			     CALL_NOSPEC
> -			     : "=a" (hv_status), ASM_CALL_CONSTRAINT,
> -			       "+c" (control), "+d" (input_address)
> -			     :  "r" (output_address),
> -				THUNK_TARGET(hv_hypercall_pg)
> -			     : "cc", "memory", "r8", "r9", "r10", "r11");
> +		__asm__ __volatile__("mov %4, %%r8\n"
> +				     CALL_NOSPEC
> +				     : "=a" (hv_status), ASM_CALL_CONSTRAINT,
> +				       "+c" (control), "+d" (input_address)
> +				     :  "r" (output_address),
> +					THUNK_TARGET(hv_hypercall_pg)
> +				     : "cc", "memory", "r8", "r9", "r10", "r11");
> +	}
>  #else
>  	u32 input_address_hi = upper_32_bits(input_address);
>  	u32 input_address_lo = lower_32_bits(input_address);
> @@ -104,7 +113,13 @@ static inline u64 _hv_do_fast_hypercall8(u64 control, u64 input1)
>  	u64 hv_status;
>  
>  #ifdef CONFIG_X86_64
> -	{
> +	if (hv_isolation_type_en_snp()) {
> +		__asm__ __volatile__(
> +				"vmmcall"
> +				: "=a" (hv_status), ASM_CALL_CONSTRAINT,
> +				"+c" (control), "+d" (input1)
> +				:: "cc", "r8", "r9", "r10", "r11");
> +	} else {
>  		__asm__ __volatile__(CALL_NOSPEC
>  				     : "=a" (hv_status), ASM_CALL_CONSTRAINT,
>  				       "+c" (control), "+d" (input1)
> @@ -149,7 +164,14 @@ static inline u64 _hv_do_fast_hypercall16(u64 control, u64 input1, u64 input2)
>  	u64 hv_status;
>  
>  #ifdef CONFIG_X86_64
> -	{
> +	if (hv_isolation_type_en_snp()) {
> +		__asm__ __volatile__("mov %4, %%r8\n"
> +				     "vmmcall"
> +				     : "=a" (hv_status), ASM_CALL_CONSTRAINT,
> +				       "+c" (control), "+d" (input1)
> +				     : "r" (input2)
> +				     : "cc", "r8", "r9", "r10", "r11");
> +	} else {
>  		__asm__ __volatile__("mov %4, %%r8\n"
>  				     CALL_NOSPEC
>  				     : "=a" (hv_status), ASM_CALL_CONSTRAINT,

-- 
Vitaly