[Devel] [PATCH hci-8.1 v4 2/5] x86/ve: enable CPUID faulting at once when the current task enters a VE

[Konstantin Khorenko]

ve_setup_task() only sets TIF_CPUID_OVERRIDE. The MSR follows the flag
in __switch_to_xtra(), so a task that enters a VE through unshare() or
setns() keeps executing CPUID natively until it is scheduled out for the
first time and sees the host values instead of the override table.

Add set_cpuid_override(), which sets the flag and, like disable_cpuid(),
flips the CPU state synchronously when the task is the current one.
Tasks set up through clone() are not running yet and are still handled
at their first switch-in.

https://virtuozzo.atlassian.net/browse/VSTOR-148843

Feature: x86: cpu pools (cpuid override)
Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
---
 arch/x86/kernel/process.c      | 12 ++++++++++++
 include/linux/cpuid_override.h |  3 +++
 kernel/ve/ve.c                 |  2 +-
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 28fc4168b6c9f..2673f2e51a833 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -23,6 +23,7 @@
 #include <linux/utsname.h>
 #include <linux/stackprotector.h>
 #include <linux/cpuidle.h>
+#include <linux/cpuid_override.h>
 #include <linux/acpi.h>
 #include <linux/elf-randomize.h>
 #include <linux/static_call.h>
@@ -381,6 +382,17 @@ static void enable_cpuid(void)
 	preempt_enable();
 }
 
+#ifdef CONFIG_VE
+void set_cpuid_override(struct task_struct *tsk)
+{
+	preempt_disable();
+	if (!test_and_set_tsk_thread_flag(tsk, TIF_CPUID_OVERRIDE) &&
+	    tsk == current)
+		set_cpuid_faulting(true);
+	preempt_enable();
+}
+#endif
+
 static int get_cpuid_mode(void)
 {
 	return !test_thread_flag(TIF_NOCPUID);
diff --git a/include/linux/cpuid_override.h b/include/linux/cpuid_override.h
index 1f5223728c9ba..83a955b628cdf 100644
--- a/include/linux/cpuid_override.h
+++ b/include/linux/cpuid_override.h
@@ -35,4 +35,7 @@ static inline bool cpuid_override_on(void)
 {
 	return rcu_access_pointer(cpuid_override);
 }
+
+struct task_struct;
+void set_cpuid_override(struct task_struct *tsk);
 #endif
diff --git a/kernel/ve/ve.c b/kernel/ve/ve.c
index 579628a8a310a..8df881039c3c6 100644
--- a/kernel/ve/ve.c
+++ b/kernel/ve/ve.c
@@ -1857,7 +1857,7 @@ void ve_setup_task(struct task_struct *task, struct ve_struct *ve)
 
 #ifdef CONFIG_X86
 	if (cpuid_override_on())
-		set_tsk_thread_flag(task, TIF_CPUID_OVERRIDE);
+		set_cpuid_override(task);
 #endif
 }
 EXPORT_SYMBOL(ve_setup_task);

-- 
2.43.0