RE: [PATCH 5/6] x86/hyperv: Support hypercalls for TDX guests

[Michael Kelley (LINUX)]

From: Dexuan Cui <decui@xxxxxxxxxxxxx> Sent: Sunday, November 27, 2022 4:59 PM
> 
> > From: Michael Kelley (LINUX) <mikelley@xxxxxxxxxxxxx>
> > Sent: Wednesday, November 23, 2022 6:45 AM
> > To: Dexuan Cui <decui@xxxxxxxxxxxxx>; ak@xxxxxxxxxxxxxxx; arnd@xxxxxxxx;
> >
> > Two thoughts:
> >
> > 1)  The #ifdef CONFIG_INTEL_TDX_GUEST could probably be removed entirely
> > with a tweak.  hv_isolation_type_tdx() already doesn't need the #ifdef asthere's
> > already a stub that returns 'false'.   Then you just need a way to handle
> > __tdx_ms_hv_hypercall(), or whatever it becomes based on the other discussion.
> > As long as you can provide a stub that does nothing, the #ifdef won't be needed.
> >
> > 2)  Assuming that we end up with some kind of Hyper-V specific version of
> > __tdx_hypercall(), and hopefully as a "C" function, could you move the handling
> > of  ms_hyperv.shared_gpa_boundary into that function?  Then you won't need
> > to break out a separate include file for struct ms_hyperv.  The Hyper-V TDX
> > hypercall function must handle both normal and "fast" hypercalls, and the
> > shared_gpa_boundary adjustment is needed only for normal hypercalls,
> > but you can check the "fast" bit in the control word to decide.
> >
> > I haven't coded these ideas, so maybe there are snags I haven't thought of.
> > But I'm really hoping we can avoid having to create a separate include
> > file for struct ms_hyperv.
> >
> > Michael
> 
> Thanks for the great suggestions! Now the code looks like this:
> (the full list of v2 patches are still WIP:
> 
> https://github.com/dcui/tdx/commits/decui/hyperv-next/2022-1121/v6.1-rc5/v2 
> 
> diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
> index 13ccb52eecd7..00e5c84e380b 100644
> --- a/arch/x86/hyperv/ivm.c
> +++ b/arch/x86/hyperv/ivm.c
> @@ -276,6 +276,27 @@ bool hv_isolation_type_tdx(void)
>  {
>  	return static_branch_unlikely(&isolation_type_tdx);
>  }
> +
> +u64 hv_tdx_hypercall(u64 control, u64 input_addr, u64 output_addr)
> +{
> +	struct tdx_hypercall_args args = { };
> +
> +	if (!(control & HV_HYPERCALL_FAST_BIT)) {
> +		if (input_addr)
> +			input_addr += ms_hyperv.shared_gpa_boundary;

At one point when working with the vTOM code, I realized that or'ing in
the shared_gpa_boundary is probably safer than add'ing it, just in case
the physical address already has vTOM set.  I don't know if that possibility
exists here, but it's something to consider as being slightly more robust.

> +
> +		if (output_addr)
> +			output_addr += ms_hyperv.shared_gpa_boundary;

Same here.

> +	}
> +
> +	args.r10 = control;
> +	args.rdx = input_addr;
> +	args.r8  = output_addr;
> +
> +	(void)__tdx_hypercall(&args, TDX_HCALL_HAS_OUTPUT);
> +
> +	return args.r11;
> +}
>  #endif
> 
>  /*
> 
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 8a2cafec4675..1be7bcf0d7d1 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -39,6 +39,8 @@ int hv_call_deposit_pages(int node, u64 partition_id, u32
> num_pages);
>  int hv_call_add_logical_proc(int node, u32 lp_index, u32 acpi_id);
>  int hv_call_create_vp(int node, u64 partition_id, u32 vp_index, u32 flags);
> 
> +u64 hv_tdx_hypercall(u64 control, u64 input_addr, u64 output_addr);
> +
>  static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
>  {
>  	u64 input_address = input ? virt_to_phys(input) : 0;
> @@ -46,6 +48,9 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void
> *output)
>  	u64 hv_status;
> 
>  #ifdef CONFIG_X86_64
> +	if (hv_isolation_type_tdx())
> +		return hv_tdx_hypercall(control, input_address, output_address);
> +
>  	if (!hv_hypercall_pg)
>  		return U64_MAX;
> 
> @@ -83,6 +88,9 @@ 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_tdx())
> +		return hv_tdx_hypercall(control, input1, 0);
> +
>  	{
>  		__asm__ __volatile__(CALL_NOSPEC
>  				     : "=a" (hv_status), ASM_CALL_CONSTRAINT,
> @@ -114,6 +122,9 @@ 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_tdx())
> +		return hv_tdx_hypercall(control, input1, input2);
> +
>  	{
>  		__asm__ __volatile__("mov %4, %%r8\n"
>  				     CALL_NOSPEC

Yes.  This new structure LGTM.

Michael