Re: [Qemu-devel] [RFC] pseries: Enable in-kernel H_LOGICAL_CI_{LOAD, STORE} implementations

[Paul Mackerras <paulus@samba.org>]

On Tue, Feb 03, 2015 at 05:10:51PM +1100, David Gibson wrote:
> qemu currently implements the hypercalls H_LOGICAL_CI_LOAD and
> H_LOGICAL_CI_STORE as PAPR extensions.  These are used by the SLOF firmware
> for IO, because performing cache inhibited MMIO accesses with the MMU off
> (real mode) is very awkward on POWER.
> 
> This approach breaks when SLOF needs to access IO devices implemented
> within KVM instead of in qemu.  The simplest example would be virtio-blk
> using an iothread, because the iothread / dataplane mechanism relies on
> an in-kernel implementation of the virtio queue notification MMIO.
> 
> To fix this, an in-kernel implementation of these hypercalls has been made,
> however, the hypercalls still need to be enabled from qemu.  This performs
> the necessary calls to do so.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

[snip]

> +    ret1 = kvmppc_enable_hcall(kvm_state, H_LOGICAL_CI_LOAD);
> +    if (ret1 != 0) {
> +        fprintf(stderr, "Warning: error enabling H_LOGICAL_CI_LOAD in KVM:"
> +                " %s\n", strerror(errno));
> +    }
> +
> +    ret2 = kvmppc_enable_hcall(kvm_state, H_LOGICAL_CI_STORE);
> +    if (ret2 != 0) {
> +        fprintf(stderr, "Warning: error enabling H_LOGICAL_CI_STORE in KVM:"
> +                " %s\n", strerror(errno));
> +     }
> +
> +    if ((ret1 != 0) || (ret2 != 0)) {
> +        fprintf(stderr, "Warning: Couldn't enable H_LOGICAL_CI_* in KVM, SLOF"
> +                " may be unable to operate devices with in-kernel emulation\n");
> +    }

You'll always get these warnings if you're running on an old (meaning
current upstream) kernel, which could be annoying.  Is there any way
to tell whether you have configured any devices which need the
in-kernel MMIO emulation and only warn if you have?

Paul.