Re: [PATCH v18 015/121] KVM: TDX: Retry SEAMCALL on the lack of entropy error

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On 1/23/2024 7:52 AM, 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>
---
v18:
- update to use struct tdx_modules_args for inputs.
---
  arch/x86/kvm/vmx/tdx_errno.h |  1 +
  arch/x86/kvm/vmx/tdx_ops.h   | 15 +++++++++++----
  2 files changed, 12 insertions(+), 4 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 0e26cf22240e..f4c16e5265f0 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>
@@ -17,14 +18,20 @@
  static inline u64 tdx_seamcall(u64 op, struct tdx_module_args *in,
  			       struct tdx_module_args *out)
  {
+	struct tdx_module_args args;
+	int retry;
  	u64 ret;
- if (out) {
+	if (!out)
+		out = &args;
+
+	/* Mimic the existing rdrand_long() to retry RDRAND_RETRY_LOOPS times. */
+	retry = RDRAND_RETRY_LOOPS;
+	do {
+		/* As __seamcall_ret() overwrites out, init out on each loop. */
  		*out = *in;
  		ret = __seamcall_ret(op, out);
-	} else
-		ret = __seamcall(op, in);
-
+	} 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.
One question is when the return code is TDX_RND_NO_ENTROPY, does the input
tdx_module_args value will be modified or not?

As mentioned by Kai in previous review, there are seamcall*() variants which
handle TDX_RND_NO_ENTROPY already.

If the input tdx_module_args is not modified by a seamcall when the return
code is TDX_RND_NO_ENTROPY, the seamcall_ret() can be used directly.

But if the input tdx_module_args could be modified by a seamcall when the
return code is TDX_RND_NO_ENTROPY, the implementations of seamcall_ret() and
seamcall_saved_ret() have problem then, because the input tdx_module_args is
not re-initialized when retry.
They need to be fixed or deleted (no one is using them currently).






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