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Message-ID: <CAAhSdy16w+98VB7+DtVJOngABu2uUDmYmqURMsRBqzvKCQfGUQ@mail.gmail.com>
Date: Mon, 5 Aug 2019 11:18:34 +0530
From: Anup Patel <anup@...infault.org>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: Anup Patel <Anup.Patel@....com>,
Palmer Dabbelt <palmer@...ive.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Radim K <rkrcmar@...hat.com>,
Daniel Lezcano <daniel.lezcano@...aro.org>,
Thomas Gleixner <tglx@...utronix.de>,
Atish Patra <Atish.Patra@....com>,
Alistair Francis <Alistair.Francis@....com>,
Damien Le Moal <Damien.LeMoal@....com>,
Christoph Hellwig <hch@...radead.org>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2 04/19] RISC-V: Add initial skeletal KVM support
On Fri, Aug 2, 2019 at 2:31 PM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 02/08/19 09:47, Anup Patel wrote:
> > +static void kvm_riscv_check_vcpu_requests(struct kvm_vcpu *vcpu)
> > +{
> > + if (kvm_request_pending(vcpu)) {
> > + /* TODO: */
> > +
> > + /*
> > + * Clear IRQ_PENDING requests that were made to guarantee
> > + * that a VCPU sees new virtual interrupts.
> > + */
> > + kvm_check_request(KVM_REQ_IRQ_PENDING, vcpu);
> > + }
> > +}
>
> This kvm_check_request can go away (as it does in patch 6).
Argh, I should have removed it in v2 itself.
Thanks for catching. I will update.
>
> > +int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> > +{
> > + int ret;
> > + unsigned long scause, stval;
>
> You need to wrap this with srcu_read_lock/srcu_read_unlock, otherwise
> stage2_page_fault can access freed memslot arrays. (ARM doesn't have
> this issue because it does not have to decode instructions on MMIO faults).
Looking at KVM ARM/ARM64, I was not sure about use of kvm->srcu. Thanks
for clarifying. I will use kvm->srcu like you suggested.
>
> That is,
>
> vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
>
> > + /* Process MMIO value returned from user-space */
> > + if (run->exit_reason == KVM_EXIT_MMIO) {
> > + ret = kvm_riscv_vcpu_mmio_return(vcpu, vcpu->run);
> > + if (ret)
> > + return ret;
> > + }
> > +
> > + if (run->immediate_exit)
> > + return -EINTR;
> > +
> > + vcpu_load(vcpu);
> > +
> > + kvm_sigset_activate(vcpu);
> > +
> > + ret = 1;
> > + run->exit_reason = KVM_EXIT_UNKNOWN;
> > + while (ret > 0) {
> > + /* Check conditions before entering the guest */
> > + cond_resched();
> > +
> > + kvm_riscv_check_vcpu_requests(vcpu);
> > +
> > + preempt_disable();
> > +
> > + local_irq_disable();
> > +
> > + /*
> > + * Exit if we have a signal pending so that we can deliver
> > + * the signal to user space.
> > + */
> > + if (signal_pending(current)) {
> > + ret = -EINTR;
> > + run->exit_reason = KVM_EXIT_INTR;
> > + }
>
> Add an srcu_read_unlock here (and then the smp_store_mb can become
> smp_mb__after_srcu_read_unlock + WRITE_ONCE).
Sure, I will update.
>
>
> > + /*
> > + * Ensure we set mode to IN_GUEST_MODE after we disable
> > + * interrupts and before the final VCPU requests check.
> > + * See the comment in kvm_vcpu_exiting_guest_mode() and
> > + * Documentation/virtual/kvm/vcpu-requests.rst
> > + */
> > + smp_store_mb(vcpu->mode, IN_GUEST_MODE);
> > +
> > + if (ret <= 0 ||
> > + kvm_request_pending(vcpu)) {
> > + vcpu->mode = OUTSIDE_GUEST_MODE;
> > + local_irq_enable();
> > + preempt_enable();
> > + continue;
> > + }
> > +
> > + guest_enter_irqoff();
> > +
> > + __kvm_riscv_switch_to(&vcpu->arch);
> > +
> > + vcpu->mode = OUTSIDE_GUEST_MODE;
> > + vcpu->stat.exits++;
> > +
> > + /* Save SCAUSE and STVAL because we might get an interrupt
> > + * between __kvm_riscv_switch_to() and local_irq_enable()
> > + * which can potentially overwrite SCAUSE and STVAL.
> > + */
> > + scause = csr_read(CSR_SCAUSE);
> > + stval = csr_read(CSR_STVAL);
> > +
> > + /*
> > + * We may have taken a host interrupt in VS/VU-mode (i.e.
> > + * while executing the guest). This interrupt is still
> > + * pending, as we haven't serviced it yet!
> > + *
> > + * We're now back in HS-mode with interrupts disabled
> > + * so enabling the interrupts now will have the effect
> > + * of taking the interrupt again, in HS-mode this time.
> > + */
> > + local_irq_enable();
> > +
> > + /*
> > + * We do local_irq_enable() before calling guest_exit() so
> > + * that if a timer interrupt hits while running the guest
> > + * we account that tick as being spent in the guest. We
> > + * enable preemption after calling guest_exit() so that if
> > + * we get preempted we make sure ticks after that is not
> > + * counted as guest time.
> > + */
> > + guest_exit();
> > +
> > + preempt_enable();
>
> And another srcu_read_lock here. Using vcpu->srcu_idx instead of a
> local variable also allows system_opcode_insn to wrap kvm_vcpu_block
> with a srcu_read_unlock/srcu_read_lock pair.
Okay.
>
> > + ret = kvm_riscv_vcpu_exit(vcpu, run, scause, stval);
> > + }
> > +
> > + kvm_sigset_deactivate(vcpu);
>
> And finally srcu_read_unlock here.
Okay.
Regards,
Anup
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