Re: [PATCH 1/2] KVM: kvm-io: support cookies

Paolo Bonzini
2013-07-03T11:47:05Z

Il 03/07/2013 13:45, Cornelia Huck ha scritto:
> On Wed, 03 Jul 2013 12:58:00 +0200
> Paolo Bonzini <pbonzini@redhat.com> wrote:
>
>> Il 03/07/2013 12:51, Cornelia Huck ha scritto:
>>> On Wed, 03 Jul 2013 11:21:23 +0200
>>> Paolo Bonzini <pbonzini@redhat.com> wrote:
>>>
>>>> Il 03/07/2013 11:05, Paolo Bonzini ha scritto:
>>>>> Nice idea, though I don't really like the duplication between
>>>>> kvm_io_bus_write and kvm_io_bus_write_cookie.
>>>>>
>>>>> Can you make kvm_io_bus_write, and perhaps kvm_io_bus_read too, return
>>>>> the cookie, and return -EINVAL here if the cookie is garbage?
>>>>
>>>> On second though---no need to return -EINVAL, you can just pass the
>>>> cookie by value and tail-call kvm_io_bus_write. Whatever makes the s390
>>>> code look nicer.
>>>
>>> It would probably be easier to have the non-cookie functions call the
>>> cookie functions with a negative cookie value, like the following
>>> (untested):
>>
>> That would work too, but it adds a small overhead to the non-cookie
>> calls. If Gleb agrees with you, it is fine; otherwise, I'd prefer that
>> one explicitly requests the cookie on input.
>
> Just to compare, I also did a patch that returns the index instead
> (equally untested). Changing the callers was straightforward; we gain
> an extra scu_dereference() in the invalid cookie case.

This looks much nicer, thanks for putting up with me!

Paolo

> From ff45cdc27e47020251f0100759adf372c19a29c4 Mon Sep 17 00:00:00 2001
> From: Cornelia Huck <cornelia.huck@de.ibm.com>
> Date: Tue, 2 Jul 2013 13:30:56 +0200
> Subject: [PATCH 1/2] KVM: kvm-io: support cookies
>
> Add new functions kvm_io_bus_{read,write}_cookie() that allows users of
> the kvm io infrastructure to use a cookie value to speed up lookup of a
> device on an io bus.
>
> kvm_io_bus_{read,write} now returns the index on the bus; existing callers
> have been fixed up to accept return codes > 0.
>
> Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
> ---
> arch/ia64/kvm/kvm-ia64.c | 2 +-
> arch/powerpc/kvm/powerpc.c | 4 ++--
> arch/x86/kvm/x86.c | 8 ++++---
> include/linux/kvm_host.h | 4 ++++
> virt/kvm/kvm_main.c | 58 +++++++++++++++++++++++++++++++++++++++++++++-
> 5 files changed, 69 insertions(+), 7 deletions(-)
>
> diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
> index 5b2dc0d..465ab54 100644
> --- a/arch/ia64/kvm/kvm-ia64.c
> +++ b/arch/ia64/kvm/kvm-ia64.c
> @@ -250,7 +250,7 @@ mmio:
> else
> r = kvm_io_bus_write(vcpu->kvm, KVM_MMIO_BUS, p->addr,
> p->size, &p->data);
> - if (r)
> + if (r < 0)
> printk(KERN_ERR"kvm: No iodevice found! addr:%lx\n", p->addr);
> p->state = STATE_IORESP_READY;
>
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 6316ee3..26c44d0 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -649,7 +649,7 @@ int kvmppc_handle_load(struct kvm_run *run, struct kvm_vcpu *vcpu,
>
> srcu_read_unlock(&vcpu->kvm->srcu, idx);
>
> - if (!ret) {
> + if (ret >= 0) {
> kvmppc_complete_mmio_load(vcpu, run);
> vcpu->mmio_needed = 0;
> return EMULATE_DONE;
> @@ -711,7 +711,7 @@ int kvmppc_handle_store(struct kvm_run *run, struct kvm_vcpu *vcpu,
>
> srcu_read_unlock(&vcpu->kvm->srcu, idx);
>
> - if (!ret) {
> + if (ret >= 0) {
> vcpu->mmio_needed = 0;
> return EMULATE_DONE;
> }
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 7d71c0f..62b325c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3860,7 +3860,8 @@ static int vcpu_mmio_write(struct kvm_vcpu *vcpu, gpa_t addr, int len,
> n = min(len, 8);
> if (!(vcpu->arch.apic &&
> !kvm_iodevice_write(&vcpu->arch.apic->dev, addr, n, v))
> - && kvm_io_bus_write(vcpu->kvm, KVM_MMIO_BUS, addr, n, v))
> + && (kvm_io_bus_write(vcpu->kvm, KVM_MMIO_BUS, addr, n, v)
> + < 0))
> break;
> handled += n;
> addr += n;
> @@ -3880,7 +3881,8 @@ static int vcpu_mmio_read(struct kvm_vcpu *vcpu, gpa_t addr, int len, void *v)
> n = min(len, 8);
> if (!(vcpu->arch.apic &&
> !kvm_iodevice_read(&vcpu->arch.apic->dev, addr, n, v))
> - && kvm_io_bus_read(vcpu->kvm, KVM_MMIO_BUS, addr, n, v))
> + && (kvm_io_bus_read(vcpu->kvm, KVM_MMIO_BUS, addr, n, v)
> + < 0))
> break;
> trace_kvm_mmio(KVM_TRACE_MMIO_READ, n, addr, *(u64 *)v);
> handled += n;
> @@ -4361,7 +4363,7 @@ static int kernel_pio(struct kvm_vcpu *vcpu, void *pd)
> r = kvm_io_bus_write(vcpu->kvm, KVM_PIO_BUS,
> vcpu->arch.pio.port, vcpu->arch.pio.size,
> pd);
> - return r;
> + return (r >= 0) ? 0 : r;
> }
>
> static int emulator_pio_in_out(struct kvm_vcpu *vcpu, int size,
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index e3aae6d..60e261c9 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -159,8 +159,12 @@ enum kvm_bus {
>
> int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> int len, const void *val);
> +int kvm_io_bus_write_cookie(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> + int len, const void *val, long cookie);
> int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr, int len,
> void *val);
> +int kvm_io_bus_read_cookie(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> + int len, void *val, long cookie);
> int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> int len, struct kvm_io_device *dev);
> int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 1580dd4..ed34f10 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2884,13 +2884,41 @@ int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> while (idx < bus->dev_count &&
> kvm_io_bus_sort_cmp(&range, &bus->range[idx]) == 0) {
> if (!kvm_iodevice_write(bus->range[idx].dev, addr, len, val))
> - return 0;
> + return idx;
> idx++;
> }
>
> return -EOPNOTSUPP;
> }
>
> +/* kvm_io_bus_write_cookie - called under kvm->slots_lock */
> +int kvm_io_bus_write_cookie(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> + int len, const void *val, long cookie)
> +{
> + struct kvm_io_bus *bus;
> + struct kvm_io_range range;
> +
> + range = (struct kvm_io_range) {
> + .addr = addr,
> + .len = len,
> + };
> +
> + bus = srcu_dereference(kvm->buses[bus_idx], &kvm->srcu);
> +
> + /* First try the device referenced by cookie. */
> + if ((cookie >= 0) && (cookie < bus->dev_count) &&
> + (kvm_io_bus_sort_cmp(&range, &bus->range[cookie]) == 0))
> + if (!kvm_iodevice_write(bus->range[cookie].dev, addr, len,
> + val))
> + return cookie;
> +
> + /*
> + * cookie contained garbage; fall back to search and return the
> + * correct cookie value.
> + */
> + return kvm_io_bus_write(kvm, bus_idx, addr, len, val);
> +}
> +
> /* kvm_io_bus_read - called under kvm->slots_lock */
> int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> int len, void *val)
> @@ -2919,6 +2947,34 @@ int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> return -EOPNOTSUPP;
> }
>
> +/* kvm_io_bus_read_cookie - called under kvm->slots_lock */
> +int kvm_io_bus_read_cookie(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> + int len, void *val, long cookie)
> +{
> + struct kvm_io_bus *bus;
> + struct kvm_io_range range;
> +
> + range = (struct kvm_io_range) {
> + .addr = addr,
> + .len = len,
> + };
> +
> + bus = srcu_dereference(kvm->buses[bus_idx], &kvm->srcu);
> +
> + /* First try the device referenced by cookie. */
> + if ((cookie >= 0) && (cookie < bus->dev_count) &&
> + (kvm_io_bus_sort_cmp(&range, &bus->range[cookie]) == 0))
> + if (!kvm_iodevice_read(bus->range[cookie].dev, addr, len,
> + val))
> + return cookie;
> +
> + /*
> + * cookie contained garbage; fall back to search and return the
> + * correct cookie value.
> + */
> + return kvm_io_bus_read(kvm, bus_idx, addr, len, val);
> +}
> +
> /* Caller must hold slots_lock. */
> int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
> int len, struct kvm_io_device *dev)
>