RE: [PATCH V3 06/13] HV: Add ghcb hvcall support for SNP VM

[Michael Kelley <mikelley@xxxxxxxxxxxxx>]

From: Tianyu Lan <ltykernel@xxxxxxxxx> Sent: Monday, August 9, 2021 10:56 AM
> 
> 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@xxxxxxxxxxxxx>
> ---
>  arch/x86/hyperv/ivm.c           | 43 +++++++++++++++++++++++++++++++++
>  arch/x86/include/asm/mshyperv.h |  1 +
>  drivers/hv/connection.c         |  6 ++++-
>  drivers/hv/hv.c                 |  8 +++++-
>  include/asm-generic/mshyperv.h  | 29 ++++++++++++++++++++++
>  5 files changed, 85 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
> index ec0e5c259740..c13ec5560d73 100644
> --- a/arch/x86/hyperv/ivm.c
> +++ b/arch/x86/hyperv/ivm.c
> @@ -15,6 +15,49 @@
>  #include <asm/io.h>
>  #include <asm/mshyperv.h>
> 
> +#define GHCB_USAGE_HYPERV_CALL       1
> +
> +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;
> +
> +     WARN_ON(in_nmi());
> +
> +     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;
> +     }
> +
> +     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;
> +}
> +EXPORT_SYMBOL_GPL(hv_ghcb_hypercall);

This function is called from architecture independent code, so it needs a
default no-op stub to enable the code to compile on ARM64.  The stub should
always return failure.

> +
>  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 730985676ea3..a30c60f189a3 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -255,6 +255,7 @@ 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 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));
> +     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 59f7173c4d9f..e5c9fc467893 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));
> +     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/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index 90dac369a2dc..400181b855c1 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -31,6 +31,35 @@
> 
>  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);

Alignment should be to HV_HYP_PAGE_SIZE.  And it would be a good safety
play to have a BUILD_BUG_ON() somewhere asserting that
sizeof(union hv_ghcb) == HV_HYP_PAGE_SIZE.

> 
>  struct ms_hyperv_info {
> --
> 2.25.1