On 05.02.15 01:53, David Gibson wrote: > On POWER, storage caching is usually configured via the MMU - attributes > such as cache-inhibited are stored in the TLB and the hashed page table. > > This makes correctly performing cache inhibited IO accesses awkward when > the MMU is turned off (real mode). Some CPU models provide special > registers to control the cache attributes of real mode load and stores but > this is not at all consistent. This is a problem in particular for SLOF, > the firmware used on KVM guests, which runs entirely in real mode, but > which needs to do IO to load the kernel. > > To simplify this qemu implements two special hypercalls, H_LOGICAL_CI_LOAD > and H_LOGICAL_CI_STORE which simulate a cache-inhibited load or store to > a logical address (aka guest physical address). SLOF uses these for IO. > > However, because these are implemented within qemu, not the host kernel, > these bypass any IO devices emulated within KVM itself. The simplest way > to see this problem is to attempt to boot a KVM guest from a virtio-blk > device with iothread / dataplane enabled. The iothread code relies on an > in kernel implementation of the virtio queue notification, which is not > triggered by the IO hcalls, and so the guest will stall in SLOF unable to > load the guest OS. > > This patch addresses this by providing in-kernel implementations of the > 2 hypercalls, which correctly scan the KVM IO bus. Any access to an > address not handled by the KVM IO bus will cause a VM exit, hitting the > qemu implementation as before. > > Note that a userspace change is also required, in order to enable these > new hcall implementations with KVM_CAP_PPC_ENABLE_HCALL. > > Signed-off-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> Thanks, applied to kvm-ppc-queue. Alex -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
