Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752022AbdHHD7Z (ORCPT ); Mon, 7 Aug 2017 23:59:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:57422 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751891AbdHHD7X (ORCPT ); Mon, 7 Aug 2017 23:59:23 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3F2D422B60 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=luto@kernel.org From: Andy Lutomirski To: X86 ML , Juergen Gross Cc: Borislav Petkov , linux-kernel@vger.kernel.org, "xen-devel@lists.xenproject.org" , Boris Ostrovsky , "H. Peter Anvin" , Andy Lutomirski Subject: [PATCH v2] x86/xen/64: Rearrange the SYSCALL entries Date: Mon, 7 Aug 2017 20:59:21 -0700 Message-Id: <7c88ed36805d36841ab03ec3b48b4122c4418d71.1502164668.git.luto@kernel.org> X-Mailer: git-send-email 2.13.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4010 Lines: 130 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. Signed-off-by: Andy Lutomirski --- Changes from v1 (which I never actually emailed): - Fix zero-extension in the compat case. arch/x86/entry/entry_64.S | 9 ++------- arch/x86/entry/entry_64_compat.S | 7 +++---- arch/x86/xen/xen-asm_64.S | 23 +++++++++-------------- 3 files changed, 14 insertions(+), 25 deletions(-) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index aa58155187c5..7cee92cf807f 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -142,14 +142,8 @@ ENTRY(entry_SYSCALL_64) * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON, * it is too small to ever cause noticeable irq latency. */ - SWAPGS_UNSAFE_STACK - /* - * A hypervisor implementation might want to use a label - * after the swapgs, so that it can do the swapgs - * for the guest and jump here on syscall. - */ -GLOBAL(entry_SYSCALL_64_after_swapgs) + swapgs movq %rsp, PER_CPU_VAR(rsp_scratch) movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp @@ -161,6 +155,7 @@ GLOBAL(entry_SYSCALL_64_after_swapgs) pushq %r11 /* pt_regs->flags */ pushq $__USER_CS /* pt_regs->cs */ pushq %rcx /* pt_regs->ip */ +GLOBAL(entry_SYSCALL_64_after_hwframe) pushq %rax /* pt_regs->orig_ax */ pushq %rdi /* pt_regs->di */ pushq %rsi /* pt_regs->si */ diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S index e1721dafbcb1..5314d7b8e5ad 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -183,21 +183,20 @@ ENDPROC(entry_SYSENTER_compat) */ ENTRY(entry_SYSCALL_compat) /* Interrupts are off on entry. */ - SWAPGS_UNSAFE_STACK + swapgs /* Stash user ESP and switch to the kernel stack. */ movl %esp, %r8d movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp - /* Zero-extending 32-bit regs, do not remove */ - movl %eax, %eax - /* Construct struct pt_regs on stack */ pushq $__USER32_DS /* pt_regs->ss */ pushq %r8 /* pt_regs->sp */ pushq %r11 /* pt_regs->flags */ pushq $__USER32_CS /* pt_regs->cs */ pushq %rcx /* pt_regs->ip */ +GLOBAL(entry_SYSCALL_compat_after_hwframe) + movl %eax, %eax /* discard orig_ax high bits */ pushq %rax /* pt_regs->orig_ax */ pushq %rdi /* pt_regs->di */ pushq %rsi /* pt_regs->si */ diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S index c3df43141e70..a8a4f4c460a6 100644 --- a/arch/x86/xen/xen-asm_64.S +++ b/arch/x86/xen/xen-asm_64.S @@ -82,34 +82,29 @@ RELOC(xen_sysret64, 1b+1) * rip * r11 * rsp->rcx - * - * In all the entrypoints, we undo all that to make it look like a - * CPU-generated syscall/sysenter and jump to the normal entrypoint. */ -.macro undo_xen_syscall - mov 0*8(%rsp), %rcx - mov 1*8(%rsp), %r11 - mov 5*8(%rsp), %rsp -.endm - /* Normal 64-bit system call target */ ENTRY(xen_syscall_target) - undo_xen_syscall - jmp entry_SYSCALL_64_after_swapgs + popq %rcx + popq %r11 + jmp entry_SYSCALL_64_after_hwframe ENDPROC(xen_syscall_target) #ifdef CONFIG_IA32_EMULATION /* 32-bit compat syscall target */ ENTRY(xen_syscall32_target) - undo_xen_syscall - jmp entry_SYSCALL_compat + popq %rcx + popq %r11 + jmp entry_SYSCALL_compat_after_hwframe ENDPROC(xen_syscall32_target) /* 32-bit compat sysenter target */ ENTRY(xen_sysenter_target) - undo_xen_syscall + mov 0*8(%rsp), %rcx + mov 1*8(%rsp), %r11 + mov 5*8(%rsp), %rsp jmp entry_SYSENTER_compat ENDPROC(xen_sysenter_target) -- 2.13.3