linux-kernel - [RFC PATCH v2 16/32] x86/fred: reserve space for the FRED stack frame

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Message-Id: <20230106085617.17248-17-xin3.li@intel.com>
Date:   Fri,  6 Jan 2023 00:56:01 -0800
From:   Xin Li <xin3.li@...el.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, peterz@...radead.org,
        andrew.cooper3@...rix.com, seanjc@...gle.com, pbonzini@...hat.com,
        ravi.v.shankar@...el.com
Subject: [RFC PATCH v2 16/32] x86/fred: reserve space for the FRED stack frame

From: "H. Peter Anvin (Intel)" <hpa@...or.com>

When using FRED, reserve space at the top of the stack frame, just
like i386 does. A future version of FRED might have dynamic frame
sizes, though, in which case it might be necessary to make
TOP_OF_KERNEL_STACK_PADDING a variable instead of a constant.

Signed-off-by: H. Peter Anvin (Intel) <hpa@...or.com>
Signed-off-by: Xin Li <xin3.li@...el.com>
---
 arch/x86/include/asm/thread_info.h | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index f0cb881c1d69..fea0e69fc3d4 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -31,7 +31,9 @@
  * In vm86 mode, the hardware frame is much longer still, so add 16
  * bytes to make room for the real-mode segments.
  *
- * x86_64 has a fixed-length stack frame.
+ * x86-64 has a fixed-length stack frame, but it depends on whether
+ * or not FRED is enabled. Future versions of FRED might make this
+ * dynamic, but for now it is always 2 words longer.
  */
 #ifdef CONFIG_X86_32
 # ifdef CONFIG_VM86
@@ -39,8 +41,12 @@
 # else
 #  define TOP_OF_KERNEL_STACK_PADDING 8
 # endif
-#else
-# define TOP_OF_KERNEL_STACK_PADDING 0
+#else /* x86-64 */
+# ifdef CONFIG_X86_FRED
+#  define TOP_OF_KERNEL_STACK_PADDING (2*8)
+# else
+#  define TOP_OF_KERNEL_STACK_PADDING 0
+# endif
 #endif
 
 /*
-- 
2.34.1