linux-kernel - Re: [RFC PATCH V2 06/18] x86/hyperv: Use vmmcall to implement hvcall in sev-snp enlightened guest

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Message-ID: <76952ed2-9fee-eae9-c9f3-5a7dd0fc1153@gmail.com>
Date:   Thu, 15 Dec 2022 00:02:44 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
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        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
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        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "jgross@...e.com" <jgross@...e.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "kirill@...temov.name" <kirill@...temov.name>,
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        <pawan.kumar.gupta@...ux.intel.com>,
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Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: [RFC PATCH V2 06/18] x86/hyperv: Use vmmcall to implement hvcall
 in sev-snp enlightened guest

On 12/14/2022 1:19 AM, Michael Kelley (LINUX) wrote:
> From: Tianyu Lan <ltykernel@...il.com> Sent: Friday, November 18, 2022 7:46 PM
>>
>> In sev-snp enlightened guest, hvcall needs to use vmmcall to trigger
> 
> What does "hvcall" refer to here?  Is this a Hyper-V hypercall, or just
> a generic hypervisor call?

It's should be Hyper-V hypercall. Will make it accurate in the next
version. Thanks for reminder.

> 
>> vmexit and notify hypervisor to handle hypercall request.
>>
>> Signed-off-by: Tianyu Lan <tiala@...rosoft.com>
>> ---
>>   arch/x86/include/asm/mshyperv.h | 66 ++++++++++++++++++++++-----------
>>   1 file changed, 45 insertions(+), 21 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
>> index 9b8c3f638845..28d5429e33c9 100644
>> --- a/arch/x86/include/asm/mshyperv.h
>> +++ b/arch/x86/include/asm/mshyperv.h
>> @@ -45,16 +45,25 @@ 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()) {
>> +		__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);
>> @@ -82,12 +91,18 @@ static inline u64 hv_do_fast_hypercall8(u16 code, u64 input1)
>>   	u64 hv_status, control = (u64)code | HV_HYPERCALL_FAST_BIT;
>>
>>   #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)
>> -				     : THUNK_TARGET(hv_hypercall_pg)
>> -				     : "cc", "r8", "r9", "r10", "r11");
>> +				: "=a" (hv_status), ASM_CALL_CONSTRAINT,
>> +				"+c" (control), "+d" (input1)
>> +				: THUNK_TARGET(hv_hypercall_pg)
>> +				: "cc", "r8", "r9", "r10", "r11");
> 
> The above 4 lines appear to just have changes in indentation.  Maybe
> there's value in having the same indentation as the new code you've
> added, so I won't object if you want to keep the changes.

OK. Will update in the next version.

> 
>>   	}
>>   #else
>>   	{
>> @@ -113,14 +128,21 @@ static inline u64 hv_do_fast_hypercall16(u16 code, u64 input1, u64 input2)
>>   	u64 hv_status, control = (u64)code | HV_HYPERCALL_FAST_BIT;
>>
>>   #ifdef CONFIG_X86_64
>> -	{
>> +	if (hv_isolation_type_en_snp()) {
>>   		__asm__ __volatile__("mov %4, %%r8\n"
>> -				     CALL_NOSPEC
>> -				     : "=a" (hv_status), ASM_CALL_CONSTRAINT,
>> -				       "+c" (control), "+d" (input1)
>> -				     : "r" (input2),
>> -				       THUNK_TARGET(hv_hypercall_pg)
>> -				     : "cc", "r8", "r9", "r10", "r11");
>> +				"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,
>> +				"+c" (control), "+d" (input1)
>> +				: "r" (input2),
>> +				THUNK_TARGET(hv_hypercall_pg)
>> +				: "cc", "r8", "r9", "r10", "r11");
>