On Thu, Feb 05, 2015 at 01:57:11AM +0100, Alexander Graf wrote: > > > 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. Any news on when this might go up to mainline? -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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