Messages in this thread | | | Subject | Re: [PATCH v2 2/7] kvm: add guest_state_{enter,exit}_irqoff() | From | Nicolas Saenz Julienne <> | Date | Fri, 21 Jan 2022 18:35:37 +0100 |
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On Wed, 2022-01-19 at 10:58 +0000, Mark Rutland wrote: > When transitioning to/from guest mode, it is necessary to inform > lockdep, tracing, and RCU in a specific order, similar to the > requirements for transitions to/from user mode. Additionally, it is > necessary to perform vtime accounting for a window around running the > guest, with RCU enabled, such that timer interrupts taken from the guest > can be accounted as guest time. > > Most architectures don't handle all the necessary pieces, and a have a > number of common bugs, including unsafe usage of RCU during the window > between guest_enter() and guest_exit(). > > On x86, this was dealt with across commits: > > 87fa7f3e98a1310e ("x86/kvm: Move context tracking where it belongs") > 0642391e2139a2c1 ("x86/kvm/vmx: Add hardirq tracing to guest enter/exit") > 9fc975e9efd03e57 ("x86/kvm/svm: Add hardirq tracing on guest enter/exit") > 3ebccdf373c21d86 ("x86/kvm/vmx: Move guest enter/exit into .noinstr.text") > 135961e0a7d555fc ("x86/kvm/svm: Move guest enter/exit into .noinstr.text") > 160457140187c5fb ("KVM: x86: Defer vtime accounting 'til after IRQ handling") > bc908e091b326467 ("KVM: x86: Consolidate guest enter/exit logic to common helpers") > > ... but those fixes are specific to x86, and as the resulting logic > (while correct) is split across generic helper functions and > x86-specific helper functions, it is difficult to see that the > entry/exit accounting is balanced. > > This patch adds generic helpers which architectures can use to handle > guest entry/exit consistently and correctly. The guest_{enter,exit}() > helpers are split into guest_timing_{enter,exit}() to perform vtime > accounting, and guest_context_{enter,exit}() to perform the necessary > context tracking and RCU management. The existing guest_{enter,exit}() > heleprs are left as wrappers of these. > > Atop this, new guest_state_enter_irqoff() and guest_state_exit_irqoff() > helpers are added to handle the ordering of lockdep, tracing, and RCU > manageent. These are inteneded to mirror exit_to_user_mode() and > enter_from_user_mode(). > > Subsequent patches will migrate architectures over to the new helpers, > following 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(); > > This sequences handles all of the above correctly, and more clearly > balances the entry and exit portions, making it easier to understand. > > The existing helpers are marked as deprecated, and will be removed once > all architectures have been converted. > > There should be no functional change as a result of this patch. > > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Reviewed-by: Marc Zyngier <maz@kernel.org> > Cc: Paolo Bonzini <pbonzini@redhat.com> > ---
Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Thanks,
-- Nicolás Sáenz
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