From: Anup Patel <anup@brainfault.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Anup Patel <Anup.Patel@wdc.com>,
Palmer Dabbelt <palmer@sifive.com>,
Paul Walmsley <paul.walmsley@sifive.com>,
Radim K <rkrcmar@redhat.com>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>,
Atish Patra <Atish.Patra@wdc.com>,
Alistair Francis <Alistair.Francis@wdc.com>,
Damien Le Moal <Damien.LeMoal@wdc.com>,
Christoph Hellwig <hch@infradead.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-riscv@lists.infradead.org"
<linux-riscv@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH v2 11/19] RISC-V: KVM: Implement VMID allocator
Date: Mon, 5 Aug 2019 15:37:12 +0530 [thread overview]
Message-ID: <CAAhSdy2y+DfV0b7dG_V43AL_MVz2R+LzEsE0y8YuiJY_EBeabg@mail.gmail.com> (raw)
In-Reply-To: <ef688903-ff49-ffeb-1f95-ef995942d5dc@redhat.com>
On Fri, Aug 2, 2019 at 2:49 PM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 02/08/19 09:48, Anup Patel wrote:
> > +struct kvm_vmid {
> > + unsigned long vmid_version;
> > + unsigned long vmid;
> > +};
> > +
>
> Please document that both fields are written under vmid_lock, and read
> outside it.
Sure, will add comments in asm/kvm_host.h
>
> > + /*
> > + * On SMP we know no other CPUs can use this CPU's or
> > + * each other's VMID after forced exit returns since the
> > + * vmid_lock blocks them from re-entry to the guest.
> > + */
> > + force_exit_and_guest_tlb_flush(cpu_all_mask);
>
> Please use kvm_flush_remote_tlbs(kvm) instead. All you need to do to
> support it is check for KVM_REQ_TLB_FLUSH and handle it by calling
> __kvm_riscv_hfence_gvma_all. Also, since your spinlock is global you
> probably should release it around the call to kvm_flush_remote_tlbs.
> (Think of an implementation that has a very small number of VMID bits).
Sure, I will use kvm_flush_remote_tlbs() here.
>
> > + if (unlikely(vmid_next == 0)) {
> > + WRITE_ONCE(vmid_version, READ_ONCE(vmid_version) + 1);
> > + vmid_next = 1;
> > + /*
> > + * On SMP we know no other CPUs can use this CPU's or
> > + * each other's VMID after forced exit returns since the
> > + * vmid_lock blocks them from re-entry to the guest.
> > + */
> > + force_exit_and_guest_tlb_flush(cpu_all_mask);
> > + }
> > +
> > + vmid->vmid = vmid_next;
> > + vmid_next++;
> > + vmid_next &= (1 << vmid_bits) - 1;
> > +
> > + /* Ensure VMID next update is completed */
> > + smp_wmb();
>
> This barrier is not necessary. Writes to vmid->vmid need not be ordered
> with writes to vmid->vmid_version, because the accesses happen in
> completely different places.
Yes, your right. There is already a WRITE_ONCE after it.
>
> (As a rule of thumb, each smp_wmb() should have a matching smp_rmb()
> somewhere, and this one doesn't).
Sure, thanks for the hint.
>
> Paolo
>
> > + WRITE_ONCE(vmid->vmid_version, READ_ONCE(vmid_version));
> > +
Regards,
Anup
next prev parent reply other threads:[~2019-08-05 10:07 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-02 7:46 [RFC PATCH v2 00/19] KVM RISC-V Support Anup Patel
2019-08-02 7:47 ` [RFC PATCH v2 01/19] KVM: RISC-V: Add KVM_REG_RISCV for ONE_REG interface Anup Patel
2019-08-02 7:47 ` [RFC PATCH v2 02/19] RISC-V: Export few kernel symbols Anup Patel
2019-08-02 7:47 ` [RFC PATCH v2 03/19] RISC-V: Add hypervisor extension related CSR defines Anup Patel
2019-08-02 7:47 ` [RFC PATCH v2 04/19] RISC-V: Add initial skeletal KVM support Anup Patel
2019-08-02 9:01 ` Paolo Bonzini
2019-08-05 5:48 ` Anup Patel
2019-08-02 7:47 ` [RFC PATCH v2 05/19] RISC-V: KVM: Implement VCPU create, init and destroy functions Anup Patel
2019-08-02 7:47 ` [RFC PATCH v2 06/19] RISC-V: KVM: Implement VCPU interrupts and requests handling Anup Patel
2019-08-02 8:17 ` Paolo Bonzini
2019-08-05 12:27 ` Anup Patel
2019-08-02 7:47 ` [RFC PATCH v2 07/19] RISC-V: KVM: Implement KVM_GET_ONE_REG/KVM_SET_ONE_REG ioctls Anup Patel
2019-08-02 9:03 ` Paolo Bonzini
2019-08-05 6:55 ` Anup Patel
2019-08-05 7:10 ` Paolo Bonzini
2019-08-05 11:00 ` Anup Patel
2019-08-05 11:07 ` Paolo Bonzini
2019-08-05 11:37 ` Christian Borntraeger
2019-08-05 11:56 ` Anup Patel
2019-08-05 12:01 ` Paolo Bonzini
2019-08-05 12:13 ` Anup Patel
2019-08-05 11:56 ` Paolo Bonzini
2019-08-02 7:47 ` [RFC PATCH v2 08/19] RISC-V: KVM: Implement VCPU world-switch Anup Patel
2019-08-02 8:30 ` Paolo Bonzini
2019-08-02 8:43 ` Anup Patel
2019-08-02 8:59 ` Paolo Bonzini
2019-08-02 7:47 ` [RFC PATCH v2 09/19] RISC-V: KVM: Handle MMIO exits for VCPU Anup Patel
2019-08-02 7:47 ` [RFC PATCH v2 10/19] RISC-V: KVM: Handle WFI " Anup Patel
2019-08-02 9:03 ` Paolo Bonzini
2019-08-05 7:12 ` Anup Patel
2019-08-05 7:14 ` Paolo Bonzini
2019-08-05 7:18 ` Anup Patel
2019-08-02 7:48 ` [RFC PATCH v2 11/19] RISC-V: KVM: Implement VMID allocator Anup Patel
2019-08-02 9:19 ` Paolo Bonzini
2019-08-05 10:07 ` Anup Patel [this message]
2019-08-02 7:48 ` [RFC PATCH v2 12/19] RISC-V: KVM: Implement stage2 page table programming Anup Patel
2019-08-02 9:14 ` Paolo Bonzini
2019-08-05 10:08 ` Anup Patel
2019-08-02 7:48 ` [RFC PATCH v2 13/19] RISC-V: KVM: Implement MMU notifiers Anup Patel
2019-08-02 7:48 ` [RFC PATCH v2 14/19] RISC-V: KVM: Add timer functionality Anup Patel
2019-08-02 7:48 ` [RFC PATCH v2 15/19] RISC-V: KVM: FP lazy save/restore Anup Patel
2019-08-02 7:48 ` [RFC PATCH v2 16/19] RISC-V: KVM: Implement ONE REG interface for FP registers Anup Patel
2019-08-02 7:48 ` [RFC PATCH v2 17/19] RISC-V: KVM: Add SBI v0.1 support Anup Patel
2019-08-02 7:48 ` [RFC PATCH v2 18/19] RISC-V: Enable VIRTIO drivers in RV64 and RV32 defconfig Anup Patel
2019-08-02 7:48 ` [RFC PATCH v2 19/19] RISC-V: KVM: Add MAINTAINERS entry Anup Patel
2019-08-02 9:22 ` [RFC PATCH v2 00/19] KVM RISC-V Support Paolo Bonzini
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