linux-kernel - [PATCH 1/2] x86/random: Retry on RDSEED failure

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Message-ID: <20240130083007.1876787-1-kirill.shutemov@linux.intel.com>
Date: Tue, 30 Jan 2024 10:30:06 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	x86@...nel.org,
	"Theodore Ts'o" <tytso@....edu>,
	"Jason A. Donenfeld" <Jason@...c4.com>
Cc: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
	Elena Reshetova <elena.reshetova@...el.com>,
	Jun Nakajima <jun.nakajima@...el.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	"Kalra, Ashish" <ashish.kalra@....com>,
	Sean Christopherson <seanjc@...gle.com>,
	linux-coco@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH 1/2] x86/random: Retry on RDSEED failure

The function rdrand_long() retries 10 times before returning failure to
the caller. On the other hand, rdseed_long() gives up on the first
failure.

According to the Intel SDM, both instructions should follow the same
retry approach. This information can be found in the section titled
"Random Number Generator Instructions".

To align the behavior of rdseed_long() with rdrand_long(), it should be
modified to retry 10 times before giving up.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 arch/x86/include/asm/archrandom.h | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/archrandom.h b/arch/x86/include/asm/archrandom.h
index 02bae8e0758b..918c5880de9e 100644
--- a/arch/x86/include/asm/archrandom.h
+++ b/arch/x86/include/asm/archrandom.h
@@ -33,11 +33,19 @@ static inline bool __must_check rdrand_long(unsigned long *v)
 
 static inline bool __must_check rdseed_long(unsigned long *v)
 {
+	unsigned int retry = RDRAND_RETRY_LOOPS;
 	bool ok;
-	asm volatile("rdseed %[out]"
-		     CC_SET(c)
-		     : CC_OUT(c) (ok), [out] "=r" (*v));
-	return ok;
+
+	do {
+		asm volatile("rdseed %[out]"
+			     CC_SET(c)
+			     : CC_OUT(c) (ok), [out] "=r" (*v));
+
+		if (ok)
+			return true;
+	} while (--retry);
+
+	return false;
 }
 
 /*
-- 
2.43.0