Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756534AbbGPVpA (ORCPT ); Thu, 16 Jul 2015 17:45:00 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:36486 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756284AbbGPVoH (ORCPT ); Thu, 16 Jul 2015 17:44:07 -0400 From: Boris Ostrovsky To: david.vrabel@citrix.com, konrad.wilk@oracle.com Cc: roger.pau@citrix.com, elena.ufimtseva@oracle.com, stefano.stabellini@eu.citrix.com, tim@xen.org, jbeulich@suse.com, andrew.cooper3@citrix.com, ian.campbell@citrix.com, ian.jackson@eu.citrix.com, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, boris.ostrovsky@oracle.com Subject: [PATCH v2 1/6] xen/x86/pvh: Save %rbx in xen_pvh_early_cpu_init() Date: Thu, 16 Jul 2015 17:43:36 -0400 Message-Id: <1437083021-24488-2-git-send-email-boris.ostrovsky@oracle.com> X-Mailer: git-send-email 1.8.1.4 In-Reply-To: <1437083021-24488-1-git-send-email-boris.ostrovsky@oracle.com> References: <1437083021-24488-1-git-send-email-boris.ostrovsky@oracle.com> X-Source-IP: userv0021.oracle.com [156.151.31.71] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4822 Lines: 142 x86-64 ABI requires that functions preserve %rbx. When xen_pvh_early_cpu_init() is executed on boot cpu it is invoked as a function and 'cpuid' instruction will clobber %rbx. (This is not a concern on secondary processors since there xen_pvh_early_cpu_init() is the entry point and thus does not need to preserve registers.) Since we cannot access stack on secondary processors (PTE's NX bit will cause #GP on AMD --- see commit a2ef5dc2c7cb ("x86/xen: Set EFER.NX and EFER.SCE in PVH guests")) we can't always save %rbx on the stack. We work around this by creating a new entry point for those processors --- xen_pvh_early_cpu_init_secondary(). Note that on secondary CPUs we will load %rbx with garbage from the stack, which is OK. As a side effect of these changes we don't need to save %rsi anymore, since we can use %rbx instead of %rsi as a temporary register. (We could store %rbx into another scratch register such as %r8 but since we will need new entry point for 32-bit PVH anyway we go with this approach for symmetry). Konrad also sugested that with separate entry point for secondary processors we don't need the second argument ('bool entry') to xen_pvh_early_cpu_init[_secondary](). So it is dropped. Signed-off-by: Boris Ostrovsky --- Changes in v2: * Dropped second argument to xen_pvh_early_cpu_init() arch/x86/xen/enlighten.c | 2 +- arch/x86/xen/smp.c | 4 ++-- arch/x86/xen/smp.h | 8 ++++++-- arch/x86/xen/xen-head.S | 27 ++++++++++++++------------- 4 files changed, 23 insertions(+), 18 deletions(-) diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c index 0b95c9b..f8dc398 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -1454,7 +1454,7 @@ static void __init xen_pvh_early_guest_init(void) xen_have_vector_callback = 1; - xen_pvh_early_cpu_init(0, false); + xen_pvh_early_cpu_init(0); xen_pvh_set_cr_flags(0); #ifdef CONFIG_X86_32 diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c index 8648438..e53be3b 100644 --- a/arch/x86/xen/smp.c +++ b/arch/x86/xen/smp.c @@ -423,9 +423,9 @@ cpu_initialize_context(unsigned int cpu, struct task_struct *idle) * bit set. This means before DS/SS is touched, NX in * EFER must be set. Hence the following assembly glue code. */ - ctxt->user_regs.eip = (unsigned long)xen_pvh_early_cpu_init; + ctxt->user_regs.eip = + (unsigned long)xen_pvh_early_cpu_init_secondary; ctxt->user_regs.rdi = cpu; - ctxt->user_regs.rsi = true; /* entry == true */ } #endif ctxt->user_regs.esp = idle->thread.sp0 - sizeof(struct pt_regs); diff --git a/arch/x86/xen/smp.h b/arch/x86/xen/smp.h index 963d62a..538c00d 100644 --- a/arch/x86/xen/smp.h +++ b/arch/x86/xen/smp.h @@ -9,9 +9,13 @@ extern void xen_send_IPI_all(int vector); extern void xen_send_IPI_self(int vector); #ifdef CONFIG_XEN_PVH -extern void xen_pvh_early_cpu_init(int cpu, bool entry); +extern void xen_pvh_early_cpu_init(int cpu); +extern void xen_pvh_early_cpu_init_secondary(int cpu); #else -static inline void xen_pvh_early_cpu_init(int cpu, bool entry) +static inline void xen_pvh_early_cpu_init(int cpu) +{ +} +static inline void xen_pvh_early_cpu_init_secondary(int cpu) { } #endif diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S index 8afdfcc..944b08b 100644 --- a/arch/x86/xen/xen-head.S +++ b/arch/x86/xen/xen-head.S @@ -53,31 +53,32 @@ ENTRY(startup_xen) /* * xen_pvh_early_cpu_init() - early PVH VCPU initialization * @cpu: this cpu number (%rdi) - * @entry: true if this is a secondary vcpu coming up on this entry - * point, false if this is the boot CPU being initialized for - * the first time (%rsi) - * - * Note: This is called as a function on the boot CPU, and is the entry point - * on the secondary CPU. */ ENTRY(xen_pvh_early_cpu_init) - mov %rsi, %r11 - + mov %rbx, -8(%rsp) + xor %esi, %esi + jmp 1f + +/* Entry point for secondary CPUs. Can't touch stack until NX is dealt with. */ +ENTRY(xen_pvh_early_cpu_init_secondary) + mov $1, %esi +1: /* Gather features to see if NX implemented. */ mov $0x80000001, %eax cpuid - mov %edx, %esi + mov %edx, %ebx mov $MSR_EFER, %ecx rdmsr bts $_EFER_SCE, %eax - bt $20, %esi - jnc 1f /* No NX, skip setting it */ + bt $20, %ebx + jnc 2f /* No NX, skip setting it */ bts $_EFER_NX, %eax -1: wrmsr +2: wrmsr + mov -8(%rsp), %rbx #ifdef CONFIG_SMP - cmp $0, %r11b + cmp $0, %esi jne cpu_bringup_and_idle #endif ret -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/