Hi Peter,

On 19/08/16 13:53, Peter Maydell wrote:

On 19 August 2016 at 13:38, Marc Zyngier [off-list ref] wrote:

quoted

So far, we've been disabling KVM on systems where the GICV region couldn't
be safely given to a guest. Now that we're able to handle this access
safely by emulating it in HYP, we can enable this feature when we detect
an unsafe configuration.

Signed-off-by: Marc Zyngier <redacted>
---
 virt/kvm/arm/vgic/vgic-v2.c | 69 +++++++++++++++++++++++++++------------------
 1 file changed, 42 insertions(+), 27 deletions(-)

diff --git a/virt/kvm/arm/vgic/vgic-v2.c b/virt/kvm/arm/vgic/vgic-v2.c
index b8da901..d1dcfc76 100644
--- a/virt/kvm/arm/vgic/vgic-v2.c
+++ b/virt/kvm/arm/vgic/vgic-v2.c

@@ -278,12 +278,14 @@ int vgic_v2_map_resources(struct kvm *kvm)
                goto out;
        }

-       ret = kvm_phys_addr_ioremap(kvm, dist->vgic_cpu_base,
-                                   kvm_vgic_global_state.vcpu_base,
-                                   KVM_VGIC_V2_CPU_SIZE, true);
-       if (ret) {
-               kvm_err("Unable to remap VGIC CPU to VCPU\n");
-               goto out;
+       if (!static_branch_unlikely(&vgic_v2_cpuif_trap)) {
+               ret = kvm_phys_addr_ioremap(kvm, dist->vgic_cpu_base,
+                                           kvm_vgic_global_state.vcpu_base,
+                                           KVM_VGIC_V2_CPU_SIZE, true);
+               if (ret) {
+                       kvm_err("Unable to remap VGIC CPU to VCPU\n");
+                       goto out;
+               }
        }

        dist->ready = true;

@@ -312,45 +314,51 @@ int vgic_v2_probe(const struct gic_kvm_info *info)
                return -ENXIO;
        }

-       if (!PAGE_ALIGNED(info->vcpu.start)) {
-               kvm_err("GICV physical address 0x%llx not page aligned\n",
-                       (unsigned long long)info->vcpu.start);
-               return -ENXIO;
-       }
+       if (!PAGE_ALIGNED(info->vcpu.start) ||
+           !PAGE_ALIGNED(resource_size(&info->vcpu))) {
+               kvm_info("GICV region size/alignement is unsafe, using trapping\n");

"alignment".

Ah, thanks. There's always a bit of French being stuck somewhere... ;-)

Is it worth specifically saying "performance will be worse", or do we
expect this to only happen on systems where the h/w can't permit direct
access (as opposed to those with bad dt info) ?

We cannot distinguish between the two, unfortunately. Even worse, ACPI
only gives us a base address, and not the size of the region. So even if
the HW was perfectly compliant with SBSA, we have to assume the worse case.

I guess that a slightly more alarming message is in order indeed.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...