From: Miroslav Benes <mbenes@suse.cz>
To: boris.ostrovsky@oracle.com, jgross@suse.com,
sstabellini@kernel.org, tglx@linutronix.de, mingo@redhat.com,
bp@alien8.de, hpa@zytor.com, jpoimboe@redhat.com
Cc: x86@kernel.org, xen-devel@lists.xenproject.org,
linux-kernel@vger.kernel.org, live-patching@vger.kernel.org,
jslaby@suse.cz, Miroslav Benes <mbenes@suse.cz>
Subject: [RFC PATCH 2/2] x86/xen: Make the secondary CPU idle tasks reliable
Date: Thu, 12 Mar 2020 15:20:07 +0100 [thread overview]
Message-ID: <20200312142007.11488-3-mbenes@suse.cz> (raw)
In-Reply-To: <20200312142007.11488-1-mbenes@suse.cz>
The unwinder reports the secondary CPU idle tasks' stack on XEN PV as
unreliable, which affects at least live patching.
cpu_initialize_context() sets up the context of the CPU through
VCPUOP_initialise hypercall. After it is woken up, the idle task starts
in cpu_bringup_and_idle() function and its stack starts at the offset
right below pt_regs. The unwinder correctly detects the end of stack
there but it is confused by NULL return address in the last frame.
RFC: I haven't found the way to teach the unwinder about the state of
the stack there. Thus the ugly hack using assembly. Similar to what
startup_xen() has got for boot CPU.
It introduces objtool "unreachable instruction" warning just right after
the jump to cpu_bringup_and_idle(). It should show the idea what needs
to be done though, I think. Ideas welcome.
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
---
arch/x86/xen/smp_pv.c | 3 ++-
arch/x86/xen/xen-head.S | 10 ++++++++++
2 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index 802ee5bba66c..6b88cdcbef8f 100644
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -53,6 +53,7 @@ static DEFINE_PER_CPU(struct xen_common_irq, xen_irq_work) = { .irq = -1 };
static DEFINE_PER_CPU(struct xen_common_irq, xen_pmu_irq) = { .irq = -1 };
static irqreturn_t xen_irq_work_interrupt(int irq, void *dev_id);
+extern unsigned char asm_cpu_bringup_and_idle[];
static void cpu_bringup(void)
{
@@ -309,7 +310,7 @@ cpu_initialize_context(unsigned int cpu, struct task_struct *idle)
* pointing just below where pt_regs would be if it were a normal
* kernel entry.
*/
- ctxt->user_regs.eip = (unsigned long)cpu_bringup_and_idle;
+ ctxt->user_regs.eip = (unsigned long)asm_cpu_bringup_and_idle;
ctxt->flags = VGCF_IN_KERNEL;
ctxt->user_regs.eflags = 0x1000; /* IOPL_RING1 */
ctxt->user_regs.ds = __USER_DS;
diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index 642f346bfe02..c9a9c0bb79ed 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -56,6 +56,16 @@ SYM_CODE_START(startup_xen)
1:
SYM_CODE_END(startup_xen)
__FINIT
+
+.pushsection .text
+SYM_CODE_START(asm_cpu_bringup_and_idle)
+ UNWIND_HINT_EMPTY
+
+ push $1f
+ jmp cpu_bringup_and_idle
+1:
+SYM_CODE_END(asm_cpu_bringup_and_idle)
+.popsection
#endif
.pushsection .text
--
2.25.1
next prev parent reply other threads:[~2020-03-12 14:20 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-12 14:20 [PATCH 0/2] x86/xen: Make idle tasks reliable Miroslav Benes
2020-03-12 14:20 ` [PATCH 1/2] x86/xen: Make the boot CPU idle task reliable Miroslav Benes
2020-03-12 15:04 ` [Xen-devel] " Andrew Cooper
2020-03-12 15:17 ` Miroslav Benes
2020-03-16 14:33 ` Boris Ostrovsky
2020-03-17 9:13 ` Miroslav Benes
2020-03-12 14:20 ` Miroslav Benes [this message]
2020-03-13 8:26 ` [RFC PATCH 2/2] x86/xen: Make the secondary CPU idle tasks reliable Jürgen Groß
2020-03-13 9:54 ` Miroslav Benes
2020-03-16 15:51 ` Miroslav Benes
2020-03-16 20:35 ` Josh Poimboeuf
2020-03-17 9:16 ` Miroslav Benes
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