RE: [PATCH v2 5/6] x86/hyperv: Support hypercalls for TDX guests

["Michael Kelley (LINUX)" <mikelley@microsoft.com>]

From: Dexuan Cui <decui@microsoft.com> Sent: Tuesday, December 6, 2022 4:33 PM
> 
> A TDX guest uses the GHCI call rather than hv_hypercall_pg.
> 
> In hv_do_hypercall(), Hyper-V requires that the input/output addresses
> must have the cc_mask.

Is it a requirement that the input/output addresses refer to guest memory
pages that have marked as shared/decrypted?  For example, I don't see
any code to mark the hyperv_pcpu_input_arg page as shared/decrypted.
Do the use cases for the hyperv_pcpu_input_arg page just not occur in a
TDX VM?

Michael

> 
> Signed-off-by: Dexuan Cui <decui@microsoft.com>
> 
> ---
> 
> Changes in v2:
>   Implemented hv_tdx_hypercall() in C rather than in assembly code.
>   Renamed the parameter names of hv_tdx_hypercall().
>   Used cc_mkdec() directly in hv_do_hypercall().
> 
>  arch/x86/hyperv/hv_init.c       |  8 ++++++++
>  arch/x86/hyperv/ivm.c           | 14 ++++++++++++++
>  arch/x86/include/asm/mshyperv.h | 17 +++++++++++++++++
>  3 files changed, 39 insertions(+)
> 
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index a823fde1ad7f..c0ba53ad8b8e 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -430,6 +430,10 @@ void __init hyperv_init(void)
>  	/* Hyper-V requires to write guest os id via ghcb in SNP IVM. */
>  	hv_ghcb_msr_write(HV_X64_MSR_GUEST_OS_ID, guest_id);
> 
> +	/* A TDX guest uses the GHCI call rather than hv_hypercall_pg. */
> +	if (hv_isolation_type_tdx())
> +		goto skip_hypercall_pg_init;
> +
>  	hv_hypercall_pg = __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START,
>  			VMALLOC_END, GFP_KERNEL, PAGE_KERNEL_ROX,
>  			VM_FLUSH_RESET_PERMS, NUMA_NO_NODE,
> @@ -469,6 +473,7 @@ void __init hyperv_init(void)
>  		wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
>  	}
> 
> +skip_hypercall_pg_init:
>  	/*
>  	 * hyperv_init() is called before LAPIC is initialized: see
>  	 * apic_intr_mode_init() -> x86_platform.apic_post_init() and
> @@ -604,6 +609,9 @@ bool hv_is_hyperv_initialized(void)
>  	if (x86_hyper_type != X86_HYPER_MS_HYPERV)
>  		return false;
> 
> +	/* A TDX guest uses the GHCI call rather than hv_hypercall_pg. */
> +	if (hv_isolation_type_tdx())
> +		return true;
>  	/*
>  	 * Verify that earlier initialization succeeded by checking
>  	 * that the hypercall page is setup
> diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
> index 13ccb52eecd7..07e4253b5809 100644
> --- a/arch/x86/hyperv/ivm.c
> +++ b/arch/x86/hyperv/ivm.c
> @@ -276,6 +276,20 @@ bool hv_isolation_type_tdx(void)
>  {
>  	return static_branch_unlikely(&isolation_type_tdx);
>  }
> +
> +u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2)
> +{
> +	struct tdx_hypercall_args args = { };
> +
> +	args.r10 = control;
> +	args.rdx = param1;
> +	args.r8  = param2;
> +
> +	(void)__tdx_hypercall(&args, TDX_HCALL_HAS_OUTPUT);
> +
> +	return args.r11;
> +}
> +EXPORT_SYMBOL_GPL(hv_tdx_hypercall);
>  #endif
> 
>  /*
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 8a2cafec4675..a4d665472d9e 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -10,6 +10,7 @@
>  #include <asm/nospec-branch.h>
>  #include <asm/paravirt.h>
>  #include <asm/mshyperv.h>
> +#include <asm/coco.h>
> 
>  union hv_ghcb;
> 
> @@ -39,6 +40,12 @@ 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 param1, u64 param2);
> +
> +/*
> + * If the hypercall involves no input or output parameters, the hypervisor
> + * ignores the corresponding GPA pointer.
> + */
>  static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
>  {
>  	u64 input_address = input ? virt_to_phys(input) : 0;
> @@ -46,6 +53,10 @@ 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,
> +					cc_mkdec(input_address),
> +					cc_mkdec(output_address));
>  	if (!hv_hypercall_pg)
>  		return U64_MAX;
> 
> @@ -83,6 +94,9 @@ 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 +128,9 @@ 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
> --
> 2.25.1