diff options
| author | Thomas Gleixner <tglx@linutronix.de> | 2025-10-27 09:44:28 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2025-11-04 08:30:23 +0100 |
| commit | 83409986f49f17b14a675f9c598ad50d4c60191b (patch) | |
| tree | 59efe6d5d76c099ea7914d015a7f7e2e1185350e /virt | |
| parent | d923739e2e356424cc566143a3323c62cd6ed067 (diff) | |
rseq, virt: Retrigger RSEQ after vcpu_run()
Hypervisors invoke resume_user_mode_work() before entering the guest, which
clears TIF_NOTIFY_RESUME. The @regs argument is NULL as there is no user
space context available to them, so the rseq notify handler skips
inspecting the critical section, but updates the CPU/MM CID values
unconditionally so that the eventual pending rseq event is not lost on the
way to user space.
This is a pointless exercise as the task might be rescheduled before
actually returning to user space and it creates unnecessary work in the
vcpu_run() loops.
It's way more efficient to ignore that invocation based on @regs == NULL
and let the hypervisors re-raise TIF_NOTIFY_RESUME after returning from the
vcpu_run() loop before returning from the ioctl().
This ensures that a pending RSEQ update is not lost and the IDs are updated
before returning to user space.
Once the RSEQ handling is decoupled from TIF_NOTIFY_RESUME, this turns into
a NOOP.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Sean Christopherson <seanjc@google.com>
Link: https://patch.msgid.link/20251027084306.399495855@linutronix.de
Diffstat (limited to 'virt')
| -rw-r--r-- | virt/kvm/kvm_main.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index b7a0ae2a7b20..4255fcf9c6e5 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -49,6 +49,7 @@ #include <linux/lockdep.h> #include <linux/kthread.h> #include <linux/suspend.h> +#include <linux/rseq.h> #include <asm/processor.h> #include <asm/ioctl.h> @@ -4476,6 +4477,12 @@ static long kvm_vcpu_ioctl(struct file *filp, r = kvm_arch_vcpu_ioctl_run(vcpu); vcpu->wants_to_run = false; + /* + * FIXME: Remove this hack once all KVM architectures + * support the generic TIF bits, i.e. a dedicated TIF_RSEQ. + */ + rseq_virt_userspace_exit(); + trace_kvm_userspace_exit(vcpu->run->exit_reason, r); break; } |