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

[Paolo Bonzini <pbonzini@redhat.com>]

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)
>