Re: [RFC PATCH 5/12] HV: Add ghcb hvcall support for SNP VM

[Tianyu Lan <ltykernel@gmail.com>]

On 3/4/2021 1:21 AM, Vitaly Kuznetsov wrote:
> Tianyu Lan <ltykernel@gmail.com> writes:
> 
>> From: Tianyu Lan <Tianyu.Lan@microsoft.com>
>>
>> Hyper-V provides ghcb hvcall to handle VMBus
>> HVCALL_SIGNAL_EVENT and HVCALL_POST_MESSAGE
>> msg in SNP Isolation VM. Add such support.
>>
>> Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
>> ---
>>   arch/x86/hyperv/ivm.c           | 69 +++++++++++++++++++++++++++++++++
>>   arch/x86/include/asm/mshyperv.h |  1 +
>>   drivers/hv/connection.c         |  6 ++-
>>   drivers/hv/hv.c                 |  8 +++-
>>   4 files changed, 82 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
>> index 4332bf7aaf9b..feaabcd151f5 100644
>> --- a/arch/x86/hyperv/ivm.c
>> +++ b/arch/x86/hyperv/ivm.c
>> @@ -14,8 +14,77 @@
>>   
>>   union hv_ghcb {
>>   	struct ghcb ghcb;
>> +	struct {
>> +		u64 hypercalldata[509];
>> +		u64 outputgpa;
>> +		union {
>> +			union {
>> +				struct {
>> +					u32 callcode        : 16;
>> +					u32 isfast          : 1;
>> +					u32 reserved1       : 14;
>> +					u32 isnested        : 1;
>> +					u32 countofelements : 12;
>> +					u32 reserved2       : 4;
>> +					u32 repstartindex   : 12;
>> +					u32 reserved3       : 4;
>> +				};
>> +				u64 asuint64;
>> +			} hypercallinput;
>> +			union {
>> +				struct {
>> +					u16 callstatus;
>> +					u16 reserved1;
>> +					u32 elementsprocessed : 12;
>> +					u32 reserved2         : 20;
>> +				};
>> +				u64 asunit64;
>> +			} hypercalloutput;
>> +		};
>> +		u64 reserved2;
>> +	} hypercall;
>>   } __packed __aligned(PAGE_SIZE);
>>   
>> +u64 hv_ghcb_hypercall(u64 control, void *input, void *output, u32 input_size)
>> +{
>> +	union hv_ghcb *hv_ghcb;
>> +	void **ghcb_base;
>> +	unsigned long flags;
>> +
>> +	if (!ms_hyperv.ghcb_base)
>> +		return -EFAULT;
>> +
>> +	local_irq_save(flags);
>> +	ghcb_base = (void **)this_cpu_ptr(ms_hyperv.ghcb_base);
>> +	hv_ghcb = (union hv_ghcb *)*ghcb_base;
>> +	if (!hv_ghcb) {
>> +		local_irq_restore(flags);
>> +		return -EFAULT;
>> +	}
>> +
>> +	memset(hv_ghcb, 0x00, HV_HYP_PAGE_SIZE);
>> +	hv_ghcb->ghcb.protocol_version = 1;
>> +	hv_ghcb->ghcb.ghcb_usage = 1;
>> +
>> +	hv_ghcb->hypercall.outputgpa = (u64)output;
>> +	hv_ghcb->hypercall.hypercallinput.asuint64 = 0;
>> +	hv_ghcb->hypercall.hypercallinput.callcode = control;
>> +
>> +	if (input_size)
>> +		memcpy(hv_ghcb->hypercall.hypercalldata, input, input_size);
>> +
>> +	VMGEXIT();
>> +
>> +	hv_ghcb->ghcb.ghcb_usage = 0xffffffff;
>> +	memset(hv_ghcb->ghcb.save.valid_bitmap, 0,
>> +	       sizeof(hv_ghcb->ghcb.save.valid_bitmap));
>> +
>> +	local_irq_restore(flags);
>> +
>> +	return hv_ghcb->hypercall.hypercalloutput.callstatus;
>> +}
>> +EXPORT_SYMBOL_GPL(hv_ghcb_hypercall);
>> +
>>   void hv_ghcb_msr_write(u64 msr, u64 value)
>>   {
>>   	union hv_ghcb *hv_ghcb;
>> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
>> index f624d72b99d3..c8f66d269e5b 100644
>> --- a/arch/x86/include/asm/mshyperv.h
>> +++ b/arch/x86/include/asm/mshyperv.h
>> @@ -274,6 +274,7 @@ void hv_sint_rdmsrl_ghcb(u64 msr, u64 *value);
>>   void hv_signal_eom_ghcb(void);
>>   void hv_ghcb_msr_write(u64 msr, u64 value);
>>   void hv_ghcb_msr_read(u64 msr, u64 *value);
>> +u64 hv_ghcb_hypercall(u64 control, void *input, void *output, u32 input_size);
>>   
>>   #define hv_get_synint_state_ghcb(int_num, val)			\
>>   	hv_sint_rdmsrl_ghcb(HV_X64_MSR_SINT0 + int_num, val)
>> diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
>> index c83612cddb99..79bca653dce9 100644
>> --- a/drivers/hv/connection.c
>> +++ b/drivers/hv/connection.c
>> @@ -442,6 +442,10 @@ void vmbus_set_event(struct vmbus_channel *channel)
>>   
>>   	++channel->sig_events;
>>   
>> -	hv_do_fast_hypercall8(HVCALL_SIGNAL_EVENT, channel->sig_event);
>> +	if (hv_isolation_type_snp())
>> +		hv_ghcb_hypercall(HVCALL_SIGNAL_EVENT, &channel->sig_event,
>> +				NULL, sizeof(u64));
>> +	else
>> +		hv_do_fast_hypercall8(HVCALL_SIGNAL_EVENT, channel->sig_event);
> 
> vmbus_set_event() is a hotpath so I'd suggest we introduce a static
> branch instead of checking hv_isolation_type_snp() every time.
> 

Good suggestion. Will add it in the next version. Thanks.