Re: [PATCH v2 3/7] kvm/arm64: rework guest entry logic

[Nicolas Saenz Julienne]

On Wed, 2022-01-19 at 10:58 +0000, Mark Rutland wrote:
> In kvm_arch_vcpu_ioctl_run() we enter an RCU extended quiescent state
> (EQS) by calling guest_enter_irqoff(), and unmasked IRQs prior to
> exiting the EQS by calling guest_exit(). As the IRQ entry code will not
> wake RCU in this case, we may run the core IRQ code and IRQ handler
> without RCU watching, leading to various potential problems.
> 
> Additionally, we do not inform lockdep or tracing that interrupts will
> be enabled during guest execution, which caan lead to misleading traces
> and warnings that interrupts have been enabled for overly-long periods.
> 
> This patch fixes these issues by using the new timing and context
> entry/exit helpers to ensure that interrupts are handled during guest
> vtime but with RCU watching, with a sequence:
> 
> 	guest_timing_enter_irqoff();
> 
> 	guest_state_enter_irqoff();
> 	< run the vcpu >
> 	guest_state_exit_irqoff();
> 
> 	< take any pending IRQs >
> 
> 	guest_timing_exit_irqoff();
> 
> Since instrumentation may make use of RCU, we must also ensure that no
> instrumented code is run during the EQS. I've split out the critical
> section into a new kvm_arm_enter_exit_vcpu() helper which is marked
> noinstr.
> 
> Fixes: 1b3d546daf85ed2b ("arm/arm64: KVM: Properly account for guest CPU time")
> Reported-by: Nicolas Saenz Julienne <nsaenzju@xxxxxxxxxx>
> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> Reviewed-by: Marc Zyngier <maz@xxxxxxxxxx>
> Cc: Alexandru Elisei <alexandru.elisei@xxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Frederic Weisbecker <frederic@xxxxxxxxxx>
> Cc: James Morse <james.morse@xxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Cc: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> ---

Reviewed-by: Nicolas Saenz Julienne <nsaenzju@xxxxxxxxxx>

Thanks,

-- 
Nicolás Sáenz