Live-Patching Archive on lore.kernel.org
 help / color / Atom feed
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, andrew.cooper3@citrix.com, jbeulich@suse.com,
	Miroslav Benes <mbenes@suse.cz>
Subject: [PATCH v3 2/2] x86/xen: Make the secondary CPU idle tasks reliable
Date: Thu, 26 Mar 2020 10:26:03 +0100
Message-ID: <20200326092603.7230-3-mbenes@suse.cz> (raw)
In-Reply-To: <20200326092603.7230-1-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.

Introduce a wrapper in assembly, which just calls
cpu_bringup_and_idle(). The return address is thus pushed on the stack
and the wrapper contains the annotation hint for the unwinder regarding
the stack state.

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..8fb8a50a28b4 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);
+void asm_cpu_bringup_and_idle(void);
 
 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 d63806e1ff7a..7d1c4fcbe8f7 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -58,6 +58,16 @@ SYM_CODE_START(startup_xen)
 	call xen_start_kernel
 SYM_CODE_END(startup_xen)
 	__FINIT
+
+#ifdef CONFIG_XEN_PV_SMP
+.pushsection .text
+SYM_CODE_START(asm_cpu_bringup_and_idle)
+	UNWIND_HINT_EMPTY
+
+	call cpu_bringup_and_idle
+SYM_CODE_END(asm_cpu_bringup_and_idle)
+.popsection
+#endif
 #endif
 
 .pushsection .text
-- 
2.25.1


  parent reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-26  9:26 [PATCH v3 0/2] x86/xen: Make " Miroslav Benes
2020-03-26  9:26 ` [PATCH v3 1/2] x86/xen: Make the boot CPU idle task reliable Miroslav Benes
2020-03-26  9:29   ` Jürgen Groß
2020-03-26  9:26 ` Miroslav Benes [this message]
2020-03-26  9:30   ` [PATCH v3 2/2] x86/xen: Make the secondary CPU idle tasks reliable Jürgen Groß

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200326092603.7230-3-mbenes@suse.cz \
    --to=mbenes@suse.cz \
    --cc=andrew.cooper3@citrix.com \
    --cc=boris.ostrovsky@oracle.com \
    --cc=bp@alien8.de \
    --cc=hpa@zytor.com \
    --cc=jbeulich@suse.com \
    --cc=jgross@suse.com \
    --cc=jpoimboe@redhat.com \
    --cc=jslaby@suse.cz \
    --cc=linux-kernel@vger.kernel.org \
    --cc=live-patching@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=sstabellini@kernel.org \
    --cc=tglx@linutronix.de \
    --cc=x86@kernel.org \
    --cc=xen-devel@lists.xenproject.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Live-Patching Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/live-patching/0 live-patching/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 live-patching live-patching/ https://lore.kernel.org/live-patching \
		live-patching@vger.kernel.org
	public-inbox-index live-patching

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.live-patching


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git