On Mon, 18 Jun 2018 16:36:05 +1000
David Gibson <da...@gibson.dropbear.id.au> wrote:
> KVM HV has some limitations (deriving from the hardware) that mean not all
> host-cpu supported pagesizes may be usable in the guest. At present this
> means that KVM guests and TCG guests may see different available page sizes
> even if they notionally have the same vcpu model. This is confusing and
> also prevents migration between TCG and KVM.
>
> This patch makes the environment consistent by always allowing the same set
> of pagesizes. Since we can't remove the KVM limitations, we do this by
> always applying the same limitations it has, even to TCG guests.
>
> Signed-off-by: David Gibson <da...@gibson.dropbear.id.au>
> ---
> hw/ppc/spapr_caps.c | 33 +++++++++++++++++++++++++++++++++
> 1 file changed, 33 insertions(+)
>
> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
> index 9fc739b3f5..0584c7c6ab 100644
> --- a/hw/ppc/spapr_caps.c
> +++ b/hw/ppc/spapr_caps.c
> @@ -334,6 +334,38 @@ static void cap_hpt_maxpagesize_apply(sPAPRMachineState
> *spapr,
> spapr_check_pagesize(spapr, qemu_getrampagesize(), errp);
> }
>
> +static bool spapr_pagesize_cb(void *opaque, uint32_t seg_pshift, uint32_t
> pshift)
> +{
> + unsigned maxshift = *((unsigned *)opaque);
> +
> + assert(pshift >= seg_pshift);
> +
> + /* Don't allow the guest to use pages bigger than the configured
> + * maximum size */
> + if (pshift > maxshift) {
> + return false;
> + }
> +
> + /* For whatever reason, KVM doesn't allow multiple pagesizes
> + * within a segment, *except* for the case of 16M pages in a 4k or
> + * 64k segment. Always exclude other cases, so that TCG and KVM
> + * guests see a consistent environment */
Unless I'm missing something, I don't see how we could get "other cases"
with TCG, at least with the current content of ppc_hash64_opts_POWER7.
> + if ((pshift != seg_pshift) && (pshift != 24)) {
> + return false;
> + }
> +
> + return true;
> +}
> +
> +static void cap_hpt_maxpagesize_cpu_apply(sPAPRMachineState *spapr,
> + PowerPCCPU *cpu,
> + uint8_t val, Error **errp)
> +{
> + unsigned maxshift = val;
> +
> + ppc_hash64_filter_pagesizes(cpu, spapr_pagesize_cb, &maxshift);
> +}
> +
> sPAPRCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
> [SPAPR_CAP_HTM] = {
> .name = "htm",
> @@ -401,6 +433,7 @@ sPAPRCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
> .set = spapr_cap_set_pagesize,
> .type = "int",
> .apply = cap_hpt_maxpagesize_apply,
> + .cpu_apply = cap_hpt_maxpagesize_cpu_apply,
> },
> };
>
