Re: [PATCH v17 012/116] KVM: TDX: Retry SEAMCALL on the lack of entropy error

[Huang, Kai]

On Tue, 2023-11-07 at 06:55 -0800, isaku.yamahata@xxxxxxxxx wrote:
> From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> 
> Some SEAMCALL may return TDX_RND_NO_ENTROPY error when the entropy is
> lacking.  Retry SEAMCALL on the error following rdrand_long() to retry
> RDRAND_RETRY_LOOPS times.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> ---
>  arch/x86/kvm/vmx/tdx_errno.h |  1 +
>  arch/x86/kvm/vmx/tdx_ops.h   | 40 +++++++++++++++++++++---------------
>  2 files changed, 24 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/tdx_errno.h b/arch/x86/kvm/vmx/tdx_errno.h
> index 7f96696b8e7c..bb093e292fef 100644
> --- a/arch/x86/kvm/vmx/tdx_errno.h
> +++ b/arch/x86/kvm/vmx/tdx_errno.h
> @@ -14,6 +14,7 @@
>  #define TDX_OPERAND_INVALID			0xC000010000000000ULL
>  #define TDX_OPERAND_BUSY			0x8000020000000000ULL
>  #define TDX_PREVIOUS_TLB_EPOCH_BUSY		0x8000020100000000ULL
> +#define TDX_RND_NO_ENTROPY			0x8000020300000000ULL
>  #define TDX_VCPU_NOT_ASSOCIATED			0x8000070200000000ULL
>  #define TDX_KEY_GENERATION_FAILED		0x8000080000000000ULL
>  #define TDX_KEY_STATE_INCORRECT			0xC000081100000000ULL
> diff --git a/arch/x86/kvm/vmx/tdx_ops.h b/arch/x86/kvm/vmx/tdx_ops.h
> index 12fd6b8d49e0..a55977626ae3 100644
> --- a/arch/x86/kvm/vmx/tdx_ops.h
> +++ b/arch/x86/kvm/vmx/tdx_ops.h
> @@ -6,6 +6,7 @@
>  
>  #include <linux/compiler.h>
>  
> +#include <asm/archrandom.h>
>  #include <asm/cacheflush.h>
>  #include <asm/asm.h>
>  #include <asm/kvm_host.h>
> @@ -17,25 +18,30 @@
>  static inline u64 tdx_seamcall(u64 op, u64 rcx, u64 rdx, u64 r8, u64 r9,
>  			       struct tdx_module_args *out)
>  {
> +	int retry;
>  	u64 ret;
>  
> -	if (out) {
> -		*out = (struct tdx_module_args) {
> -			.rcx = rcx,
> -			.rdx = rdx,
> -			.r8 = r8,
> -			.r9 = r9,
> -		};
> -		ret = __seamcall_ret(op, out);
> -	} else {
> -		struct tdx_module_args args = {
> -			.rcx = rcx,
> -			.rdx = rdx,
> -			.r8 = r8,
> -			.r9 = r9,
> -		};
> -		ret = __seamcall(op, &args);
> -	}
> +	/* Mimic the existing rdrand_long() to retry RDRAND_RETRY_LOOPS times. */
> +	retry = RDRAND_RETRY_LOOPS;
> +	do {
> +		if (out) {
> +			*out = (struct tdx_module_args) {
> +				.rcx = rcx,
> +				.rdx = rdx,
> +				.r8 = r8,
> +				.r9 = r9,
> +			};
> +			ret = __seamcall_ret(op, out);
> +		} else {
> +			struct tdx_module_args args = {
> +				.rcx = rcx,
> +				.rdx = rdx,
> +				.r8 = r8,
> +				.r9 = r9,
> +			};
> +			ret = __seamcall(op, &args);
> +		}
> +	} while (unlikely(ret == TDX_RND_NO_ENTROPY) && --retry);
>  	if (unlikely(ret == TDX_SEAMCALL_UD)) {
>  		/*
>  		 * SEAMCALLs fail with TDX_SEAMCALL_UD returned when VMX is off.

Why we cannot use seamcall*() variants directly which already handles running
out of entropy error?