Messages in this thread | | | Date | Mon, 26 Mar 2012 11:21:58 +0200 | From | Avi Kivity <> | Subject | Re: [PATCH RFC dontapply] kvm_para: add mmio word store hypercall |
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On 03/26/2012 12:05 AM, Michael S. Tsirkin wrote: > We face a dilemma: IO mapped addresses are legacy, > so, for example, PCI express bridges waste 4K > of this space for each link, in effect limiting us > to 16 devices using this space. > > Memory is supposed to replace them, but memory > exits are much slower than PIO because of the need for > emulation and page walks. > > As a solution, this patch adds an MMIO hypercall with > the guest physical address + data. > > I did test that this works but didn't benchmark yet. > > TODOs: > This only implements a 2 bytes write since this is > the minimum required for virtio, but we'll probably need > at least 1 byte reads (for ISR read). > We can support up to 8 byte reads/writes for 64 bit > guests and up to 4 bytes for 32 ones - better limit > to 4 bytes for everyone for consistency, or support > the maximum that we can?
Let's support the maximum we can.
> > static int handle_invd(struct kvm_vcpu *vcpu) > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 9cbfc06..7bc00ae 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -4915,7 +4915,9 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu) > > int kvm_emulate_hypercall(struct kvm_vcpu *vcpu) > { > + struct kvm_run *run = vcpu->run; > unsigned long nr, a0, a1, a2, a3, ret; > + gpa_t gpa; > int r = 1; > > if (kvm_hv_hypercall_enabled(vcpu->kvm)) > @@ -4946,12 +4948,24 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu) > case KVM_HC_VAPIC_POLL_IRQ: > ret = 0; > break; > + case KVM_HC_MMIO_STORE_WORD:
HC_MEMORY_WRITE
> + gpa = hc_gpa(vcpu, a1, a2); > + if (!write_mmio(vcpu, gpa, 2, &a0) && run) {
What's this && run thing?
> + run->exit_reason = KVM_EXIT_MMIO; > + run->mmio.phys_addr = gpa; > + memcpy(run->mmio.data, &a0, 2); > + run->mmio.len = 2; > + run->mmio.is_write = 1; > + r = 0; > + } > + goto noret;
What if the address is in RAM?
Note the guest can't tell if a piece of memory is direct mapped or implemented as mmio.
-- error compiling committee.c: too many arguments to function
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