[kvm-unit-tests PATCH 0/3] x86: Use macros for selectors in asm

[kvm-unit-tests PATCH 0/3] x86: Use macros for selectors in asm

[Sean Christopherson]

Use macros for segment selectors in assembly instead of open coded literals.

v2:
 - Commit to using __ASSEMBLER__.

v1: https://lore.kernel.org/all/20240621122640.2347541-1-darcy.sh@antgroup.com


Hang SU (1):
  x86: replace segment selector magic number with macro definition

Sean Christopherson (2):
  x86: Move descriptor table selector #defines to the top of desc.h
  x86: Commit to using __ASSEMBLER__ instead of __ASSEMBLY__

 lib/x86/asm/page.h |   4 +-
 lib/x86/desc.h     | 123 +++++++++++++++++++++++----------------------
 x86/cstart64.S     |   8 +--
 x86/trampolines.S  |   8 +--
 4 files changed, 75 insertions(+), 68 deletions(-)


base-commit: f77fb696cfd0e4a5562cdca189be557946bf522f
-- 
2.48.1.601.g30ceb7b040-goog

[kvm-unit-tests PATCH 1/3] x86: Move descriptor table selector #defines to the top of desc.h

[Sean Christopherson]

Hoist the selector #defines in desc.h to the very top so that they can be
exposed to assembly code with minimal #ifdefs.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 lib/x86/desc.h | 114 ++++++++++++++++++++++++-------------------------
 1 file changed, 57 insertions(+), 57 deletions(-)

diff --git a/lib/x86/desc.h b/lib/x86/desc.h
index 92c45a48..a4459127 100644
--- a/lib/x86/desc.h
+++ b/lib/x86/desc.h
@@ -1,7 +1,61 @@
 #ifndef _X86_DESC_H_
 #define _X86_DESC_H_
 
-#include <setjmp.h>
+/*
+ * selector     32-bit                        64-bit
+ * 0x00         NULL descriptor               NULL descriptor
+ * 0x08         ring-0 code segment (32-bit)  ring-0 code segment (64-bit)
+ * 0x10         ring-0 data segment (32-bit)  ring-0 data segment (32/64-bit)
+ * 0x18         ring-0 code segment (P=0)     ring-0 code segment (64-bit, P=0)
+ * 0x20         intr_alt_stack TSS            ring-0 code segment (32-bit)
+ * 0x28         ring-0 code segment (16-bit)  same
+ * 0x30         ring-0 data segment (16-bit)  same
+ * 0x38 (0x3b)  ring-3 code segment (32-bit)  same
+ * 0x40 (0x43)  ring-3 data segment (32-bit)  ring-3 data segment (32/64-bit)
+ * 0x48 (0x4b)  **unused**                    ring-3 code segment (64-bit)
+ * 0x50-0x78    free to use for test cases    same
+ * 0x80-0x870   primary TSS (CPU 0..254)      same
+ * 0x878-0x1068 percpu area (CPU 0..254)      not used
+ *
+ * Note that the same segment can be used for 32-bit and 64-bit data segments
+ * (the L bit is only defined for code segments)
+ *
+ * Selectors 0x08-0x10 and 0x3b-0x4b are set up for use with the SYSCALL
+ * and SYSRET instructions.
+ */
+
+#define KERNEL_CS   0x08
+#define KERNEL_DS   0x10
+#define NP_SEL      0x18
+#ifdef __x86_64__
+#define KERNEL_CS32 0x20
+#else
+#define TSS_INTR    0x20
+#endif
+#define KERNEL_CS16 0x28
+#define KERNEL_DS16 0x30
+#define USER_CS32   0x3b
+#define USER_DS     0x43
+#ifdef __x86_64__
+#define USER_CS64   0x4b
+#endif
+
+/* Synonyms */
+#define KERNEL_DS32 KERNEL_DS
+#define USER_DS32   USER_DS
+
+#ifdef __x86_64__
+#define KERNEL_CS64 KERNEL_CS
+#define USER_CS     USER_CS64
+#define KERNEL_DS64 KERNEL_DS
+#define USER_DS64   USER_DS
+#else
+#define KERNEL_CS32 KERNEL_CS
+#define USER_CS     USER_CS32
+#endif
+
+#define FIRST_SPARE_SEL 0x50
+#define TSS_MAIN 0x80
 
 #ifdef __ASSEMBLY__
 #define __ASM_FORM(x, ...)	x,## __VA_ARGS__
@@ -15,6 +69,8 @@
 #define __ASM_SEL(a,b)		__ASM_FORM(b)
 #endif
 
+#include <setjmp.h>
+
 void setup_idt(void);
 void load_idt(void);
 void setup_alt_stack(void);
@@ -120,62 +176,6 @@ fep_unavailable:
 	return false;
 }
 
-/*
- * selector     32-bit                        64-bit
- * 0x00         NULL descriptor               NULL descriptor
- * 0x08         ring-0 code segment (32-bit)  ring-0 code segment (64-bit)
- * 0x10         ring-0 data segment (32-bit)  ring-0 data segment (32/64-bit)
- * 0x18         ring-0 code segment (P=0)     ring-0 code segment (64-bit, P=0)
- * 0x20         intr_alt_stack TSS            ring-0 code segment (32-bit)
- * 0x28         ring-0 code segment (16-bit)  same
- * 0x30         ring-0 data segment (16-bit)  same
- * 0x38 (0x3b)  ring-3 code segment (32-bit)  same
- * 0x40 (0x43)  ring-3 data segment (32-bit)  ring-3 data segment (32/64-bit)
- * 0x48 (0x4b)  **unused**                    ring-3 code segment (64-bit)
- * 0x50-0x78    free to use for test cases    same
- * 0x80-0x870   primary TSS (CPU 0..254)      same
- * 0x878-0x1068 percpu area (CPU 0..254)      not used
- *
- * Note that the same segment can be used for 32-bit and 64-bit data segments
- * (the L bit is only defined for code segments)
- *
- * Selectors 0x08-0x10 and 0x3b-0x4b are set up for use with the SYSCALL
- * and SYSRET instructions.
- */
-
-#define KERNEL_CS   0x08
-#define KERNEL_DS   0x10
-#define NP_SEL      0x18
-#ifdef __x86_64__
-#define KERNEL_CS32 0x20
-#else
-#define TSS_INTR    0x20
-#endif
-#define KERNEL_CS16 0x28
-#define KERNEL_DS16 0x30
-#define USER_CS32   0x3b
-#define USER_DS     0x43
-#ifdef __x86_64__
-#define USER_CS64   0x4b
-#endif
-
-/* Synonyms */
-#define KERNEL_DS32 KERNEL_DS
-#define USER_DS32   USER_DS
-
-#ifdef __x86_64__
-#define KERNEL_CS64 KERNEL_CS
-#define USER_CS     USER_CS64
-#define KERNEL_DS64 KERNEL_DS
-#define USER_DS64   USER_DS
-#else
-#define KERNEL_CS32 KERNEL_CS
-#define USER_CS     USER_CS32
-#endif
-
-#define FIRST_SPARE_SEL 0x50
-#define TSS_MAIN 0x80
-
 typedef struct {
 	unsigned short offset0;
 	unsigned short selector;
-- 
2.48.1.601.g30ceb7b040-goog

[kvm-unit-tests PATCH 2/3] x86: Commit to using __ASSEMBLER__ instead of __ASSEMBLY__

[Sean Christopherson]

Convert all two of x86's anti-assembly #ifdefs from __ASSEMBLY__ to
__ASSEMBLER__.  Usage of __ASSEMBLY__ was inherited blindly from the Linux
kernel, and must be manually defined, e.g. through build rules or with
explicit #defines in assembly code.  __ASSEMBLER__ on the other hand is
automatically defined by the compiler when preprocessing assembly, i.e.
doesn't require manually #defines for the code to function correctly.

Convert only x86 for the time being, as x86 doesn't actually rely on
__ASSEMBLY__ (a clever observer will note that it's never #defined on x86).
E.g. trying to include x86's page.h doesn't work as is.  All other
architectures actually rely on __ASSEMBLY__, and will be dealt with
separately.

Note, while only gcc appears to officially document __ASSEMBLER__, clang
has followed suit since at least clang 6.0, and clang 6.0 doesn't come
remotely close to being able to comple KVM-Unit-Tests.

Link: https://gcc.gnu.org/onlinedocs/cpp/Standard-Predefined-Macros.html#Standard-Predefined-Macros
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 lib/x86/asm/page.h | 4 ++--
 lib/x86/desc.h     | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/x86/asm/page.h b/lib/x86/asm/page.h
index 298e7e8e..bc0e78c7 100644
--- a/lib/x86/asm/page.h
+++ b/lib/x86/asm/page.h
@@ -15,7 +15,7 @@ typedef unsigned long pgd_t;
 
 #include <asm-generic/page.h>
 
-#ifndef __ASSEMBLY__
+#ifndef __ASSEMBLER__
 
 #define PAGE_ALIGN(addr)        ALIGN(addr, PAGE_SIZE)
 
@@ -79,5 +79,5 @@ extern unsigned long long get_amd_sev_addr_upperbound(void);
 #define PGDIR_BITS(lvl)        (((lvl) - 1) * PGDIR_WIDTH + PAGE_SHIFT)
 #define PGDIR_OFFSET(va, lvl)  (((va) >> PGDIR_BITS(lvl)) & PGDIR_MASK)
 
-#endif /* !__ASSEMBLY__ */
+#endif /* !__ASSEMBLER__ */
 #endif
diff --git a/lib/x86/desc.h b/lib/x86/desc.h
index a4459127..aa6213d1 100644
--- a/lib/x86/desc.h
+++ b/lib/x86/desc.h
@@ -57,7 +57,7 @@
 #define FIRST_SPARE_SEL 0x50
 #define TSS_MAIN 0x80
 
-#ifdef __ASSEMBLY__
+#ifdef __ASSEMBLER__
 #define __ASM_FORM(x, ...)	x,## __VA_ARGS__
 #else
 #define __ASM_FORM(x, ...)	" " xstr(x,##__VA_ARGS__) " "
-- 
2.48.1.601.g30ceb7b040-goog

[kvm-unit-tests PATCH 3/3] x86: replace segment selector magic number with macro definition

[Sean Christopherson]

From: Hang SU <darcysail@gmail.com>

Add assembly check in desc.h, to replace segment selector
magic number with macro definition.

Signed-off-by: Hang SU <darcy.sh@antgroup.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 lib/x86/desc.h    | 7 ++++++-
 x86/cstart64.S    | 8 ++++----
 x86/trampolines.S | 8 +++++---
 3 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/lib/x86/desc.h b/lib/x86/desc.h
index aa6213d1..5634de94 100644
--- a/lib/x86/desc.h
+++ b/lib/x86/desc.h
@@ -69,6 +69,8 @@
 #define __ASM_SEL(a,b)		__ASM_FORM(b)
 #endif
 
+#ifndef __ASSEMBLER__
+
 #include <setjmp.h>
 
 void setup_idt(void);
@@ -338,4 +340,7 @@ do {									\
 
 #define asm_safe_report_ex __asm_safe_report
 
-#endif
+
+#endif /* __ASSEMBLER__ */
+
+#endif /* _X86_DESC_H_ */
diff --git a/x86/cstart64.S b/x86/cstart64.S
index 4dff1102..2b14c076 100644
--- a/x86/cstart64.S
+++ b/x86/cstart64.S
@@ -1,5 +1,5 @@
-
 #include "apic-defs.h"
+#include "desc.h"
 
 ipi_vector = 0x20
 
@@ -66,7 +66,7 @@ start:
 	mov $stacktop, %esp
 	setup_percpu_area
 	call prepare_64
-	jmpl $8, $start64
+	jmpl $KERNEL_CS, $start64
 
 switch_to_5level:
 	/* Disable CR4.PCIDE */
@@ -86,11 +86,11 @@ switch_to_5level:
 	bts $12, %eax
 	mov %eax, %cr4
 
-	mov $0x10, %ax
+	mov $KERNEL_DS, %ax
 	mov %ax, %ss
 
 	call enter_long_mode
-	jmpl $8, $lvl5
+	jmpl $KERNEL_CS, $lvl5
 
 smp_stacktop:	.long stacktop - 4096
 
diff --git a/x86/trampolines.S b/x86/trampolines.S
index 6a3df9c1..f0b05ab5 100644
--- a/x86/trampolines.S
+++ b/x86/trampolines.S
@@ -3,6 +3,8 @@
  * transition from 32-bit to 64-bit code (x86-64 only)
  */
 
+#include "desc.h"
+
  /* EFI provides it's own SIPI sequence to handle relocation. */
 #ifndef CONFIG_EFI
 .code16
@@ -15,7 +17,7 @@ sipi_entry:
 	or $1, %eax
 	mov %eax, %cr0
 	lgdtl ap_rm_gdt_descr - sipi_entry
-	ljmpl $8, $ap_start32
+	ljmpl $KERNEL_CS32, $ap_start32
 sipi_end:
 
 .globl ap_rm_gdt_descr
@@ -66,7 +68,7 @@ MSR_GS_BASE = 0xc0000101
 	mov $MSR_GS_BASE, %ecx
 	rdmsr
 
-	mov $0x10, %bx
+	mov $KERNEL_DS, %bx
 	mov %bx, %ds
 	mov %bx, %es
 	mov %bx, %fs
@@ -123,7 +125,7 @@ ap_start32:
 	call prepare_64
 
 	load_absolute_addr $ap_start64, %edx
-	pushl $0x08
+	pushl $KERNEL_CS
 	pushl %edx
 	lretl
 #endif
-- 
2.48.1.601.g30ceb7b040-goog

Re: [kvm-unit-tests PATCH 3/3] x86: replace segment selector magic number with macro definition

[Sean Christopherson]

On Fri, Feb 21, 2025, Sean Christopherson wrote:
> @@ -15,7 +17,7 @@ sipi_entry:
>  	or $1, %eax
>  	mov %eax, %cr0
>  	lgdtl ap_rm_gdt_descr - sipi_entry
> -	ljmpl $8, $ap_start32
> +	ljmpl $KERNEL_CS32, $ap_start32

Gah, this is wrong, it should be KERNEL_CS, not KERNEL_CS32.  It was wrong in the
original posting as well.  Not sure how I missed it the first time around.

I'll fixup when applying.

Re: [kvm-unit-tests PATCH 0/3] x86: Use macros for selectors in asm

[Sean Christopherson]

On Fri, 21 Feb 2025 14:54:03 -0800, Sean Christopherson wrote:
> Use macros for segment selectors in assembly instead of open coded literals.
> 
> v2:
>  - Commit to using __ASSEMBLER__.
> 
> v1: https://lore.kernel.org/all/20240621122640.2347541-1-darcy.sh@antgroup.com
> 
> [...]

Applied to kvm-x86 next (and now pulled by Paolo), with the fixup to use KERNEL_CS
instead of KERNEL_CS32.

[1/3] x86: Move descriptor table selector #defines to the top of desc.h
      https://github.com/kvm-x86/kvm-unit-tests/commit/4c5d37137baf
[2/3] x86: Commit to using __ASSEMBLER__ instead of __ASSEMBLY__
      https://github.com/kvm-x86/kvm-unit-tests/commit/f372d35fb1be
[3/3] x86: replace segment selector magic number with macro definition
      https://github.com/kvm-x86/kvm-unit-tests/commit/c8a8a35827d7

--
https://github.com/kvm-x86/kvm-unit-tests/tree/next