From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: x86@kernel.org, linux-arch@vger.kernel.org,
Will Deacon <will@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
Mark Rutland <mark.rutland@arm.com>,
Kees Cook <keescook@chromium.org>,
Keno Fischer <keno@juliacomputing.com>,
Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org,
Gabriel Krisman Bertazi <krisman@collabora.com>
Subject: [patch V4 08/15] x86/entry: Move user return notifier out of loop
Date: Tue, 21 Jul 2020 12:57:14 +0200 [thread overview]
Message-ID: <20200721110809.106972388@linutronix.de> (raw)
In-Reply-To: 20200721105706.030914876@linutronix.de
Guests and user space share certain MSRs. KVM sets these MSRs to guest
values once and does not set them back to user space values on every VM
exit to spare the costly MSR operations.
User return notifiers ensure that these MSRs are set back to the correct
values before returning to user space in exit_to_usermode_loop().
There is no reason to evaluate the TIF flag indicating that user return
notifiers need to be invoked in the loop. The important point is that they
are invoked before returning to user space.
Move the invocation out of the loop into the section which does the last
preperatory steps before returning to user space. That section is not
preemptible and runs with interrupts disabled until the actual return.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V4: New patch
---
arch/x86/entry/common.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -208,7 +208,7 @@ static long syscall_trace_enter(struct p
#define EXIT_TO_USERMODE_LOOP_FLAGS \
(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
- _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_PATCH_PENDING)
+ _TIF_NEED_RESCHED | _TIF_PATCH_PENDING)
static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
{
@@ -242,9 +242,6 @@ static void exit_to_usermode_loop(struct
rseq_handle_notify_resume(NULL, regs);
}
- if (cached_flags & _TIF_USER_RETURN_NOTIFY)
- fire_user_return_notifiers();
-
/* Disable IRQs and retry */
local_irq_disable();
@@ -273,6 +270,9 @@ static void __prepare_exit_to_usermode(s
/* Reload ti->flags; we may have rescheduled above. */
cached_flags = READ_ONCE(ti->flags);
+ if (cached_flags & _TIF_USER_RETURN_NOTIFY)
+ fire_user_return_notifiers();
+
if (unlikely(cached_flags & _TIF_IO_BITMAP))
tss_update_io_bitmap();
next prev parent reply other threads:[~2020-07-21 11:08 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-21 10:57 [patch V4 00/15] entry, x86, kvm: Generic entry/exit functionality for host and guest Thomas Gleixner
2020-07-21 10:57 ` [patch V4 01/15] seccomp: Provide stub for __secure_computing() Thomas Gleixner
2020-07-21 21:21 ` Kees Cook
2020-07-21 10:57 ` [patch V4 02/15] entry: Provide generic syscall entry functionality Thomas Gleixner
2020-07-21 21:38 ` Kees Cook
2020-07-22 7:34 ` Thomas Gleixner
2020-07-22 7:54 ` peterz
2020-07-21 10:57 ` [patch V4 03/15] entry: Provide generic syscall exit function Thomas Gleixner
2020-07-27 22:37 ` Andy Lutomirski
2020-07-21 10:57 ` [patch V4 04/15] entry: Provide generic interrupt entry/exit code Thomas Gleixner
2020-07-27 22:39 ` Andy Lutomirski
2020-07-29 12:18 ` Thomas Gleixner
2020-07-21 10:57 ` [patch V4 05/15] entry: Provide infrastructure for work before exiting to guest mode Thomas Gleixner
2020-07-21 10:57 ` [patch V4 06/15] x86/entry: Consolidate check_user_regs() Thomas Gleixner
2020-07-27 22:39 ` Andy Lutomirski
2020-07-21 10:57 ` [patch V4 07/15] x86/entry: Consolidate 32/64 bit syscall entry Thomas Gleixner
2020-07-21 10:57 ` Thomas Gleixner [this message]
2020-07-21 10:57 ` [patch V4 09/15] x86/ptrace: Provide pt_regs helper for entry/exit Thomas Gleixner
2020-07-21 10:57 ` [patch V4 10/15] x86/entry: Use generic syscall entry function Thomas Gleixner
2020-07-21 21:47 ` Kees Cook
2020-07-22 18:25 ` Thomas Gleixner
2020-07-21 10:57 ` [patch V4 11/15] x86/entry: Use generic syscall exit functionality Thomas Gleixner
2020-07-21 21:47 ` Kees Cook
2020-07-21 10:57 ` [patch V4 12/15] x86/entry: Cleanup idtentry_entry/exit_user Thomas Gleixner
2020-07-21 21:48 ` Kees Cook
2020-07-21 10:57 ` [patch V4 13/15] x86/entry: Use generic interrupt entry/exit code Thomas Gleixner
2020-07-21 10:57 ` [patch V4 14/15] x86/entry: Cleanup idtentry_enter/exit Thomas Gleixner
2020-07-21 21:48 ` Kees Cook
2020-07-21 10:57 ` [patch V4 15/15] x86/kvm: Use generic exit to guest work function Thomas Gleixner
2020-07-21 20:27 ` Sean Christopherson
2020-07-22 7:40 ` Thomas Gleixner
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