RE: [PATCH V4 06/13] hyperv: Add ghcb hvcall support for SNP VM

[Michael Kelley <mikelley@microsoft.com>]

From: Tianyu Lan <ltykernel@gmail.com> Sent: Friday, August 27, 2021 10:21 AM
> 

Subject line tag should probably be "x86/hyperv:" since the majority
of the code added is under arch/x86.

> hyperv 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>
> ---
> Change since v3:
> 	* Add hv_ghcb_hypercall() stub function to avoid
> 	  compile error for ARM.
> ---
>  arch/x86/hyperv/ivm.c          | 71 ++++++++++++++++++++++++++++++++++
>  drivers/hv/connection.c        |  6 ++-
>  drivers/hv/hv.c                |  8 +++-
>  drivers/hv/hv_common.c         |  6 +++
>  include/asm-generic/mshyperv.h |  1 +
>  5 files changed, 90 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
> index f56fe4f73000..e761c67e2218 100644
> --- a/arch/x86/hyperv/ivm.c
> +++ b/arch/x86/hyperv/ivm.c
> @@ -17,10 +17,81 @@
>  #include <asm/io.h>
>  #include <asm/mshyperv.h>
> 
> +#define GHCB_USAGE_HYPERV_CALL	1
> +
>  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(HV_HYP_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 (!hv_ghcb_pg)
> +		return -EFAULT;
> +
> +	WARN_ON(in_nmi());
> +
> +	local_irq_save(flags);
> +	ghcb_base = (void **)this_cpu_ptr(hv_ghcb_pg);
> +	hv_ghcb = (union hv_ghcb *)*ghcb_base;
> +	if (!hv_ghcb) {
> +		local_irq_restore(flags);
> +		return -EFAULT;
> +	}
> +
> +	hv_ghcb->ghcb.protocol_version = GHCB_PROTOCOL_MAX;
> +	hv_ghcb->ghcb.ghcb_usage = GHCB_USAGE_HYPERV_CALL;
> +
> +	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;

The hypercall.hypercalloutput.callstatus value must be saved
in a local variable *before* the call to local_irq_restore().  Then
the local variable is the return value.  Once local_irq_restore()
is called, the GHCB page could get reused.

> +}
> +
>  void hv_ghcb_msr_write(u64 msr, u64 value)
>  {
>  	union hv_ghcb *hv_ghcb;
> diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
> index 5e479d54918c..6d315c1465e0 100644
> --- a/drivers/hv/connection.c
> +++ b/drivers/hv/connection.c
> @@ -447,6 +447,10 @@ 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));

Better to use "sizeof(channel->sig_event)" instead of explicitly coding
the type.

> +	else
> +		hv_do_fast_hypercall8(HVCALL_SIGNAL_EVENT, channel->sig_event);
>  }
>  EXPORT_SYMBOL_GPL(vmbus_set_event);
> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
> index 97b21256a9db..d4531c64d9d3 100644
> --- a/drivers/hv/hv.c
> +++ b/drivers/hv/hv.c
> @@ -98,7 +98,13 @@ int hv_post_message(union hv_connection_id connection_id,
>  	aligned_msg->payload_size = payload_size;
>  	memcpy((void *)aligned_msg->payload, payload, payload_size);
> 
> -	status = hv_do_hypercall(HVCALL_POST_MESSAGE, aligned_msg, NULL);
> +	if (hv_isolation_type_snp())
> +		status = hv_ghcb_hypercall(HVCALL_POST_MESSAGE,
> +				(void *)aligned_msg, NULL,
> +				sizeof(struct hv_input_post_message));

As above, use "sizeof(*aligned_msg)".

> +	else
> +		status = hv_do_hypercall(HVCALL_POST_MESSAGE,
> +				aligned_msg, NULL);
> 
>  	/* Preemption must remain disabled until after the hypercall
>  	 * so some other thread can't get scheduled onto this cpu and
> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
> index 1fc82d237161..7be173a99f27 100644
> --- a/drivers/hv/hv_common.c
> +++ b/drivers/hv/hv_common.c
> @@ -289,3 +289,9 @@ void __weak hyperv_cleanup(void)
>  {
>  }
>  EXPORT_SYMBOL_GPL(hyperv_cleanup);
> +
> +u64 __weak hv_ghcb_hypercall(u64 control, void *input, void *output, u32 input_size)
> +{
> +	return HV_STATUS_INVALID_PARAMETER;
> +}
> +EXPORT_SYMBOL_GPL(hv_ghcb_hypercall);
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index 04a687d95eac..0da45807c36a 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -250,6 +250,7 @@ bool hv_is_hibernation_supported(void);
>  enum hv_isolation_type hv_get_isolation_type(void);
>  bool hv_is_isolation_supported(void);
>  bool hv_isolation_type_snp(void);
> +u64 hv_ghcb_hypercall(u64 control, void *input, void *output, u32 input_size);
>  void hyperv_cleanup(void);
>  bool hv_query_ext_cap(u64 cap_query);
>  #else /* CONFIG_HYPERV */
> --
> 2.25.1