[PATCH v4 22/23] KVM: s390: Enable 1M pages for gmap

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

While userspace is allowed to have pages of any size, the new gmap
would always use 4k pages to back the guest.

Enable 1M pages for gmap.

This allows 1M pages to be used to back a guest when userspace is using
1M pages for the corresponding addresses (e.g. THP or hugetlbfs).

Remove the limitation that disallowed having nested guests and
hugepages at the same time.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 arch/s390/kvm/gmap.c     | 2 +-
 arch/s390/kvm/kvm-s390.c | 6 +-----
 arch/s390/kvm/pv.c       | 3 +++
 3 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/s390/kvm/gmap.c b/arch/s390/kvm/gmap.c
index 502012c0dfad..ef4190f56ae9 100644
--- a/arch/s390/kvm/gmap.c
+++ b/arch/s390/kvm/gmap.c
@@ -591,7 +591,7 @@ static inline bool gmap_2g_allowed(struct gmap *gmap, gfn_t gfn)
 
 static inline bool gmap_1m_allowed(struct gmap *gmap, gfn_t gfn)
 {
-	return false;
+	return gmap->allow_hpage_1m;
 }
 
 int gmap_link(struct kvm_s390_mmu_cache *mc, struct gmap *gmap, struct guest_fault *f)
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index c8662177c63c..b7dc1d601fb8 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -849,6 +849,7 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
 			r = -EINVAL;
 		else {
 			r = 0;
+			WRITE_ONCE(kvm->arch.gmap->allow_hpage_1m, 1);
 			/*
 			 * We might have to create fake 4k page
 			 * tables. To avoid that the hardware works on
@@ -5837,11 +5838,6 @@ static int __init kvm_s390_init(void)
 		return -ENODEV;
 	}
 
-	if (nested && hpage) {
-		pr_info("A KVM host that supports nesting cannot back its KVM guests with huge pages\n");
-		return -EINVAL;
-	}
-
 	for (i = 0; i < 16; i++)
 		kvm_s390_fac_base[i] |=
 			stfle_fac_list[i] & nonhyp_mask(i);
diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
index d8a5c7b91148..8ea5f8d7e714 100644
--- a/arch/s390/kvm/pv.c
+++ b/arch/s390/kvm/pv.c
@@ -621,6 +621,9 @@ int kvm_s390_pv_init_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
 	uvcb.flags.ap_allow_instr = kvm->arch.model.uv_feat_guest.ap;
 	uvcb.flags.ap_instr_intr = kvm->arch.model.uv_feat_guest.ap_intr;
 
+	WRITE_ONCE(kvm->arch.gmap->allow_hpage_1m, 0);
+	gmap_split_huge_pages(kvm->arch.gmap);
+
 	cc = uv_call_sched(0, (u64)&uvcb);
 	*rc = uvcb.header.rc;
 	*rrc = uvcb.header.rrc;
-- 
2.51.1