From 69fef2e685597e51ce2103e8701e90d210ec0640 Mon Sep 17 00:00:00 2001
From: Yifan Liu <yifan1.liu@intel.com>
Date: Fri, 16 Jul 2021 15:09:00 +0800
Subject: [PATCH] hv: debug: Add hv console callback to VM-exit event

In some scenarios (e.g., nested) where lapic-pt is enabled for a vcpu
running on a pcpu hosting console timer, the hv console will be
inaccessible.

This patch adds the console callback to every VM-exit event so that the
console can still be somewhat functional under such circumstance.

Since this is VM-exit driven, the VM-exit/second can be low in certain
cases (e.g., idle or running stress workload). In extreme cases where
the guest panics/hangs, there will be no VM-exits at all.

In most cases, the shell is laggy but functional (probably enough for
debugging purpose).

Tracked-On: #6312
Signed-off-by: Yifan Liu <yifan1.liu@intel.com>
---
 hypervisor/arch/x86/guest/vmexit.c |  3 +++
 hypervisor/debug/console.c         | 22 ++++++++++++++++++++++
 hypervisor/include/debug/console.h |  2 ++
 hypervisor/release/console.c       |  1 +
 4 files changed, 28 insertions(+)

diff --git a/hypervisor/arch/x86/guest/vmexit.c b/hypervisor/arch/x86/guest/vmexit.c
index affb0237e..22e588e6f 100644
--- a/hypervisor/arch/x86/guest/vmexit.c
+++ b/hypervisor/arch/x86/guest/vmexit.c
@@ -22,6 +22,7 @@
 #include <asm/guest/vcpuid.h>
 #include <trace.h>
 #include <asm/rtcm.h>
+#include <debug/console.h>
 
 /*
  * According to "SDM APPENDIX C VMX BASIC EXIT REASONS",
@@ -292,6 +293,8 @@ int32_t vmexit_handler(struct acrn_vcpu *vcpu)
 		}
 	}
 
+	console_vmexit_callback(vcpu);
+
 	return ret;
 }
 
diff --git a/hypervisor/debug/console.c b/hypervisor/debug/console.c
index 826f1a2c4..0e5189b69 100644
--- a/hypervisor/debug/console.c
+++ b/hypervisor/debug/console.c
@@ -172,6 +172,28 @@ void console_setup_timer(void)
 	}
 }
 
+/* When lapic-pt is enabled for a vcpu working on the pcpu hosting
+ * console timer (currently BSP), we utilize vm-exits to drive the console.
+ *
+ * Note that currently this approach will result in a laggy shell when
+ * the number of VM-exits/second is low (which is mostly true when lapic-pt is
+ * enabled).
+ */
+void console_vmexit_callback(struct acrn_vcpu *vcpu)
+{
+	static uint64_t prev_tsc = 0;
+	uint64_t tsc;
+
+	/* console_setup_timer is called on BSP only. */
+	if ((pcpuid_from_vcpu(vcpu) == BSP_CPU_ID) && (is_lapic_pt_enabled(vcpu))) {
+		tsc = cpu_ticks();
+		if (tsc - prev_tsc > (TICKS_PER_MS * CONSOLE_KICK_TIMER_TIMEOUT)) {
+			console_timer_callback(NULL);
+			prev_tsc = tsc;
+		}
+	}
+}
+
 void suspend_console(void)
 {
 	del_timer(&console_timer);
diff --git a/hypervisor/include/debug/console.h b/hypervisor/include/debug/console.h
index 9819c1a41..768cb854b 100644
--- a/hypervisor/include/debug/console.h
+++ b/hypervisor/include/debug/console.h
@@ -8,6 +8,7 @@
 #define CONSOLE_H
 
 #include <vuart.h>
+#include <asm/guest/vcpu.h>
 
 /** Initializes the console module.
  *
@@ -35,6 +36,7 @@ void console_putc(const char *ch);
 char console_getc(void);
 
 void console_setup_timer(void);
+void console_vmexit_callback(struct acrn_vcpu *vcpu);
 
 void suspend_console(void);
 void resume_console(void);
diff --git a/hypervisor/release/console.c b/hypervisor/release/console.c
index 7866bca06..910fc7c36 100644
--- a/hypervisor/release/console.c
+++ b/hypervisor/release/console.c
@@ -27,6 +27,7 @@ void suspend_console(void) {}
 void resume_console(void) {}
 
 bool handle_dbg_cmd(__unused const char *cmd, __unused int32_t len) { return false; }
+void console_vmexit_callback(__unused struct acrn_vcpu *vcpu) {}
 
 void shell_init(void) {}
 void shell_kick(void) {}