KVM: s390: Refactor and split some gmap helpers

Refactor some gmap functions; move the implementation into a separate
file with only helper functions. The new helper functions work on vm
addresses, leaving all gmap logic in the gmap functions, which mostly
become just wrappers.

The whole gmap handling is going to be moved inside KVM soon, but the
helper functions need to touch core mm functions, and thus need to
stay in the core of kernel.

Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Reviewed-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
Acked-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20250528095502.226213-4-imbrenda@linux.ibm.com
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-ID: <20250528095502.226213-4-imbrenda@linux.ibm.com>

2 files changed, 29 insertions, 6 deletions

diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c
index 74f73141f9b9..53233dec8cad 100644
--- a/arch/s390/kvm/diag.c
+++ b/arch/s390/kvm/diag.c
@@ -11,12 +11,30 @@
 #include <linux/kvm.h>
 #include <linux/kvm_host.h>
 #include <asm/gmap.h>
+#include <asm/gmap_helpers.h>
 #include <asm/virtio-ccw.h>
 #include "kvm-s390.h"
 #include "trace.h"
 #include "trace-s390.h"
 #include "gaccess.h"
 
+static void do_discard_gfn_range(struct kvm_vcpu *vcpu, gfn_t gfn_start, gfn_t gfn_end)
+{
+	struct kvm_memslot_iter iter;
+	struct kvm_memory_slot *slot;
+	struct kvm_memslots *slots;
+	unsigned long start, end;
+
+	slots = kvm_vcpu_memslots(vcpu);
+
+	kvm_for_each_memslot_in_gfn_range(&iter, slots, gfn_start, gfn_end) {
+		slot = iter.slot;
+		start = __gfn_to_hva_memslot(slot, max(gfn_start, slot->base_gfn));
+		end = __gfn_to_hva_memslot(slot, min(gfn_end, slot->base_gfn + slot->npages));
+		gmap_helper_discard(vcpu->kvm->mm, start, end);
+	}
+}
+
 static int diag_release_pages(struct kvm_vcpu *vcpu)
 {
 	unsigned long start, end;
@@ -32,12 +50,13 @@ static int diag_release_pages(struct kvm_vcpu *vcpu)
 
 	VCPU_EVENT(vcpu, 5, "diag release pages %lX %lX", start, end);
 
+	mmap_read_lock(vcpu->kvm->mm);
 	/*
 	 * We checked for start >= end above, so lets check for the
 	 * fast path (no prefix swap page involved)
 	 */
 	if (end <= prefix || start >= prefix + 2 * PAGE_SIZE) {
-		gmap_discard(vcpu->arch.gmap, start, end);
+		do_discard_gfn_range(vcpu, gpa_to_gfn(start), gpa_to_gfn(end));
 	} else {
 		/*
 		 * This is slow path.  gmap_discard will check for start
@@ -45,13 +64,14 @@ static int diag_release_pages(struct kvm_vcpu *vcpu)
 		 * prefix and let gmap_discard make some of these calls
 		 * NOPs.
 		 */
-		gmap_discard(vcpu->arch.gmap, start, prefix);
+		do_discard_gfn_range(vcpu, gpa_to_gfn(start), gpa_to_gfn(prefix));
 		if (start <= prefix)
-			gmap_discard(vcpu->arch.gmap, 0, PAGE_SIZE);
+			do_discard_gfn_range(vcpu, 0, 1);
 		if (end > prefix + PAGE_SIZE)
-			gmap_discard(vcpu->arch.gmap, PAGE_SIZE, 2 * PAGE_SIZE);
-		gmap_discard(vcpu->arch.gmap, prefix + 2 * PAGE_SIZE, end);
+			do_discard_gfn_range(vcpu, 1, 2);
+		do_discard_gfn_range(vcpu, gpa_to_gfn(prefix) + 2, gpa_to_gfn(end));
 	}
+	mmap_read_unlock(vcpu->kvm->mm);
 	return 0;
 }
 
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 3f3175193fd7..10cfc047525d 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -40,6 +40,7 @@
 #include <asm/machine.h>
 #include <asm/stp.h>
 #include <asm/gmap.h>
+#include <asm/gmap_helpers.h>
 #include <asm/nmi.h>
 #include <asm/isc.h>
 #include <asm/sclp.h>
@@ -2674,7 +2675,9 @@ static int kvm_s390_handle_pv(struct kvm *kvm, struct kvm_pv_cmd *cmd)
 		if (r)
 			break;
 
-		r = s390_disable_cow_sharing();
+		mmap_write_lock(kvm->mm);
+		r = gmap_helper_disable_cow_sharing();
+		mmap_write_unlock(kvm->mm);
 		if (r)
 			break;