On many entries we push 8-bytes zero and exception constants are
small so we can just write a single byte saving 3 bytes for
instruction.
With ENDBR64 this reduces the size of many entry points from 32 to
16 bytes (due to alignment).
The push and the mov are overlapping stores either way. Swapping
between movl and movb will make no difference at all on performance.
Similar code is already used in autogen_stubs.
Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com>
--
v3:
- add other missing entries;
- reduce code when TRAP_syscall is used;
- improved commit message.
v2:
- added missing entry points;
- add mention to autogen_stubs code, as suggested.
---
xen/arch/x86/x86_64/entry.S | 66 ++++++++++++++++++++++---------------
1 file changed, 40 insertions(+), 26 deletions(-)
diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index ecdd6e5b47..f07e7ed3ac 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -22,6 +22,14 @@
#endif
.endm
+.macro BUILD_BUG_ON condstr cond:vararg
+ .if \cond
+ .error "Condition \condstr not satisfied"
+ .endif
+.endm
+/* preprocessor macro to make error message more user friendly */
+#define BUILD_BUG_ON(cond) BUILD_BUG_ON #cond cond
+
#ifdef CONFIG_PV
/* %rbx: struct vcpu */
FUNC_LOCAL(switch_to_kernel)
@@ -187,7 +195,8 @@ FUNC_LOCAL(restore_all_guest)
SPEC_CTRL_EXIT_TO_PV /* Req: a=spec_ctrl %rsp=regs/cpuinfo, Clob: cd */
RESTORE_ALL
- testw $TRAP_syscall,4(%rsp)
+ BUILD_BUG_ON(TRAP_syscall & 0xff)
+ testb $TRAP_syscall >> 8,4+1(%rsp)
jz iret_exit_to_guest
movq 24(%rsp),%r11 # RFLAGS
@@ -254,7 +263,8 @@ FUNC(lstar_enter)
pushq $FLAT_KERNEL_CS64
pushq %rcx
pushq $0
- movl $TRAP_syscall, 4(%rsp)
+ BUILD_BUG_ON(TRAP_syscall & 0xff)
+ movb $TRAP_syscall >> 8, 4+1(%rsp)
SAVE_ALL
SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
@@ -292,7 +302,8 @@ FUNC(cstar_enter)
pushq $FLAT_USER_CS32
pushq %rcx
pushq $0
- movl $TRAP_syscall, 4(%rsp)
+ BUILD_BUG_ON(TRAP_syscall & 0xff)
+ movb $TRAP_syscall >> 8, 4+1(%rsp)
SAVE_ALL
SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
@@ -334,7 +345,8 @@ LABEL(sysenter_eflags_saved, 0)
pushq $3 /* ring 3 null cs */
pushq $0 /* null rip */
pushq $0
- movl $TRAP_syscall, 4(%rsp)
+ BUILD_BUG_ON(TRAP_syscall & 0xff)
+ movb $TRAP_syscall >> 8, 4+1(%rsp)
SAVE_ALL
SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
@@ -389,7 +401,7 @@ FUNC(entry_int80)
ENDBR64
ALTERNATIVE "", clac, X86_FEATURE_XEN_SMAP
pushq $0
- movl $0x80, 4(%rsp)
+ movb $0x80, 4(%rsp)
SAVE_ALL
SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
@@ -561,7 +573,8 @@ __UNLIKELY_END(create_bounce_frame_bad_sp)
/* Rewrite our stack frame and return to guest-OS mode. */
/* IA32 Ref. Vol. 3: TF, VM, RF and NT flags are cleared on trap. */
/* Also clear AC: alignment checks shouldn't trigger in kernel mode. */
- orl $TRAP_syscall,UREGS_entry_vector+8(%rsp)
+ BUILD_BUG_ON(TRAP_syscall & 0xff)
+ orb $TRAP_syscall >> 8,UREGS_entry_vector+8+1(%rsp)
andl $~(X86_EFLAGS_AC|X86_EFLAGS_VM|X86_EFLAGS_RF|\
X86_EFLAGS_NT|X86_EFLAGS_TF),UREGS_eflags+8(%rsp)
movq $FLAT_KERNEL_SS,UREGS_ss+8(%rsp)
@@ -653,7 +666,7 @@ END(ret_from_intr)
.section .init.text, "ax", @progbits
FUNC(early_page_fault)
ENDBR64
- movl $X86_EXC_PF, 4(%rsp)
+ movb $X86_EXC_PF, 4(%rsp)
SAVE_ALL
movq %rsp, %rdi
call do_early_page_fault
@@ -722,7 +735,7 @@ END(common_interrupt)
FUNC(entry_PF)
ENDBR64
- movl $X86_EXC_PF, 4(%rsp)
+ movb $X86_EXC_PF, 4(%rsp)
END(entry_PF)
/* No special register assumptions. */
FUNC(handle_exception, 0)
@@ -898,105 +911,106 @@ END(handle_exception)
FUNC(entry_DE)
ENDBR64
pushq $0
- movl $X86_EXC_DE, 4(%rsp)
+ /* no need to update exception type, already 0 */
+ BUILD_BUG_ON(X86_EXC_DE)
jmp handle_exception
END(entry_DE)
FUNC(entry_MF)
ENDBR64
pushq $0
- movl $X86_EXC_MF, 4(%rsp)
+ movb $X86_EXC_MF, 4(%rsp)
jmp handle_exception
END(entry_MF)
FUNC(entry_XM)
ENDBR64
pushq $0
- movl $X86_EXC_XM, 4(%rsp)
+ movb $X86_EXC_XM, 4(%rsp)
jmp handle_exception
END(entry_XM)
FUNC(entry_NM)
ENDBR64
pushq $0
- movl $X86_EXC_NM, 4(%rsp)
+ movb $X86_EXC_NM, 4(%rsp)
jmp handle_exception
END(entry_NM)
FUNC(entry_DB)
ENDBR64
pushq $0
- movl $X86_EXC_DB, 4(%rsp)
+ movb $X86_EXC_DB, 4(%rsp)
jmp handle_ist_exception
END(entry_DB)
FUNC(entry_BP)
ENDBR64
pushq $0
- movl $X86_EXC_BP, 4(%rsp)
+ movb $X86_EXC_BP, 4(%rsp)
jmp handle_exception
END(entry_BP)
FUNC(entry_OF)
ENDBR64
pushq $0
- movl $X86_EXC_OF, 4(%rsp)
+ movb $X86_EXC_OF, 4(%rsp)
jmp handle_exception
END(entry_OF)
FUNC(entry_BR)
ENDBR64
pushq $0
- movl $X86_EXC_BR, 4(%rsp)
+ movb $X86_EXC_BR, 4(%rsp)
jmp handle_exception
END(entry_BR)
FUNC(entry_UD)
ENDBR64
pushq $0
- movl $X86_EXC_UD, 4(%rsp)
+ movb $X86_EXC_UD, 4(%rsp)
jmp handle_exception
END(entry_UD)
FUNC(entry_TS)
ENDBR64
- movl $X86_EXC_TS, 4(%rsp)
+ movb $X86_EXC_TS, 4(%rsp)
jmp handle_exception
END(entry_TS)
FUNC(entry_NP)
ENDBR64
- movl $X86_EXC_NP, 4(%rsp)
+ movb $X86_EXC_NP, 4(%rsp)
jmp handle_exception
END(entry_NP)
FUNC(entry_SS)
ENDBR64
- movl $X86_EXC_SS, 4(%rsp)
+ movb $X86_EXC_SS, 4(%rsp)
jmp handle_exception
END(entry_SS)
FUNC(entry_GP)
ENDBR64
- movl $X86_EXC_GP, 4(%rsp)
+ movb $X86_EXC_GP, 4(%rsp)
jmp handle_exception
END(entry_GP)
FUNC(entry_AC)
ENDBR64
- movl $X86_EXC_AC, 4(%rsp)
+ movb $X86_EXC_AC, 4(%rsp)
jmp handle_exception
END(entry_AC)
FUNC(entry_CP)
ENDBR64
- movl $X86_EXC_CP, 4(%rsp)
+ movb $X86_EXC_CP, 4(%rsp)
jmp handle_exception
END(entry_CP)
FUNC(entry_DF)
ENDBR64
- movl $X86_EXC_DF, 4(%rsp)
+ movb $X86_EXC_DF, 4(%rsp)
/* Set AC to reduce chance of further SMAP faults */
ALTERNATIVE "", stac, X86_FEATURE_XEN_SMAP
SAVE_ALL
@@ -1022,7 +1036,7 @@ END(entry_DF)
FUNC(entry_NMI)
ENDBR64
pushq $0
- movl $X86_EXC_NMI, 4(%rsp)
+ movb $X86_EXC_NMI, 4(%rsp)
END(entry_NMI)
FUNC(handle_ist_exception)
@@ -1158,7 +1172,7 @@ END(handle_ist_exception)
FUNC(entry_MC)
ENDBR64
pushq $0
- movl $X86_EXC_MC, 4(%rsp)
+ movb $X86_EXC_MC, 4(%rsp)
jmp handle_ist_exception
END(entry_MC)
--
2.34.1On 16.02.2024 11:50, Frediano Ziglio wrote:
> --- a/xen/arch/x86/x86_64/entry.S
> +++ b/xen/arch/x86/x86_64/entry.S
> @@ -22,6 +22,14 @@
> #endif
> .endm
>
> +.macro BUILD_BUG_ON condstr cond:vararg
> + .if \cond
> + .error "Condition \condstr not satisfied"
Maybe
.error "Condition \"\condstr\" not satisfied"
?
> @@ -187,7 +195,8 @@ FUNC_LOCAL(restore_all_guest)
> SPEC_CTRL_EXIT_TO_PV /* Req: a=spec_ctrl %rsp=regs/cpuinfo, Clob: cd */
>
> RESTORE_ALL
> - testw $TRAP_syscall,4(%rsp)
> + BUILD_BUG_ON(TRAP_syscall & 0xff)
> + testb $TRAP_syscall >> 8,4+1(%rsp)
> jz iret_exit_to_guest
Nit: Blank after comma please (and again elsewhere).
Preferably with both adjustments (which I'd be okay making while
committing, so long as you agree specifically on the former)
Reviewed-by: Jan Beulich <jbeulich@suse.com>
That said, especially with this not being an entry point path, and
neither this nor ...
> @@ -254,7 +263,8 @@ FUNC(lstar_enter)
> pushq $FLAT_KERNEL_CS64
> pushq %rcx
> pushq $0
> - movl $TRAP_syscall, 4(%rsp)
> + BUILD_BUG_ON(TRAP_syscall & 0xff)
> + movb $TRAP_syscall >> 8, 4+1(%rsp)
> SAVE_ALL
>
> SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
> @@ -292,7 +302,8 @@ FUNC(cstar_enter)
> pushq $FLAT_USER_CS32
> pushq %rcx
> pushq $0
> - movl $TRAP_syscall, 4(%rsp)
> + BUILD_BUG_ON(TRAP_syscall & 0xff)
> + movb $TRAP_syscall >> 8, 4+1(%rsp)
> SAVE_ALL
>
> SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo, %rdx=0, Clob: acd */
> @@ -334,7 +345,8 @@ LABEL(sysenter_eflags_saved, 0)
> pushq $3 /* ring 3 null cs */
> pushq $0 /* null rip */
> pushq $0
> - movl $TRAP_syscall, 4(%rsp)
> + BUILD_BUG_ON(TRAP_syscall & 0xff)
> + movb $TRAP_syscall >> 8, 4+1(%rsp)
> SAVE_ALL
... any of these being exception entry point paths (and hence none of
these changes being related to the subject), it would likely have been
a good idea to split this into two patches.
Jan
© 2016 - 2024 Red Hat, Inc.