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x86/xen/64: Rearrange the SYSCALL entries
Xen's raw SYSCALL entries are much less weird than native. Rather than fudging them to look like native entries, use the Xen-provided stack frame directly. This lets us eliminate entry_SYSCALL_64_after_swapgs and two uses of the SWAPGS_UNSAFE_STACK paravirt hook. The SYSENTER code would benefit from similar treatment. This makes one change to the native code path: the compat instruction that clears the high 32 bits of %rax is moved slightly later. I'd be surprised if this affects performance at all. Tested-by: Juergen Gross <jgross@suse.com> Signed-off-by: Andy Lutomirski <luto@kernel.org> Reviewed-by: Juergen Gross <jgross@suse.com> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: Borislav Petkov <bpetkov@suse.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: xen-devel@lists.xenproject.org Link: http://lkml.kernel.org/r/7c88ed36805d36841ab03ec3b48b4122c4418d71.1502164668.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -142,14 +142,8 @@ ENTRY(entry_SYSCALL_64)
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* We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON,
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* it is too small to ever cause noticeable irq latency.
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*/
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SWAPGS_UNSAFE_STACK
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/*
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* A hypervisor implementation might want to use a label
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* after the swapgs, so that it can do the swapgs
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* for the guest and jump here on syscall.
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*/
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GLOBAL(entry_SYSCALL_64_after_swapgs)
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swapgs
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movq %rsp, PER_CPU_VAR(rsp_scratch)
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movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
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@ -161,6 +155,7 @@ GLOBAL(entry_SYSCALL_64_after_swapgs)
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pushq %r11 /* pt_regs->flags */
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pushq $__USER_CS /* pt_regs->cs */
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pushq %rcx /* pt_regs->ip */
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GLOBAL(entry_SYSCALL_64_after_hwframe)
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pushq %rax /* pt_regs->orig_ax */
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pushq %rdi /* pt_regs->di */
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pushq %rsi /* pt_regs->si */
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@ -183,21 +183,20 @@ ENDPROC(entry_SYSENTER_compat)
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*/
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ENTRY(entry_SYSCALL_compat)
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/* Interrupts are off on entry. */
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SWAPGS_UNSAFE_STACK
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swapgs
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/* Stash user ESP and switch to the kernel stack. */
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movl %esp, %r8d
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movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
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/* Zero-extending 32-bit regs, do not remove */
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movl %eax, %eax
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/* Construct struct pt_regs on stack */
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pushq $__USER32_DS /* pt_regs->ss */
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pushq %r8 /* pt_regs->sp */
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pushq %r11 /* pt_regs->flags */
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pushq $__USER32_CS /* pt_regs->cs */
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pushq %rcx /* pt_regs->ip */
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GLOBAL(entry_SYSCALL_compat_after_hwframe)
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movl %eax, %eax /* discard orig_ax high bits */
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pushq %rax /* pt_regs->orig_ax */
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pushq %rdi /* pt_regs->di */
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pushq %rsi /* pt_regs->si */
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@ -82,34 +82,29 @@ RELOC(xen_sysret64, 1b+1)
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* rip
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* r11
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* rsp->rcx
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*
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* In all the entrypoints, we undo all that to make it look like a
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* CPU-generated syscall/sysenter and jump to the normal entrypoint.
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*/
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.macro undo_xen_syscall
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mov 0*8(%rsp), %rcx
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mov 1*8(%rsp), %r11
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mov 5*8(%rsp), %rsp
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.endm
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/* Normal 64-bit system call target */
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ENTRY(xen_syscall_target)
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undo_xen_syscall
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jmp entry_SYSCALL_64_after_swapgs
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popq %rcx
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popq %r11
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jmp entry_SYSCALL_64_after_hwframe
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ENDPROC(xen_syscall_target)
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#ifdef CONFIG_IA32_EMULATION
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/* 32-bit compat syscall target */
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ENTRY(xen_syscall32_target)
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undo_xen_syscall
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jmp entry_SYSCALL_compat
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popq %rcx
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popq %r11
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jmp entry_SYSCALL_compat_after_hwframe
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ENDPROC(xen_syscall32_target)
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/* 32-bit compat sysenter target */
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ENTRY(xen_sysenter_target)
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undo_xen_syscall
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mov 0*8(%rsp), %rcx
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mov 1*8(%rsp), %r11
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mov 5*8(%rsp), %rsp
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jmp entry_SYSENTER_compat
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ENDPROC(xen_sysenter_target)
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