[PATCH 1/4] KVM: s390: Replace get_zeroed_page() with kzalloc() for the STHYI buffer

[Mike Rapoport (Microsoft)]

handle_sthyi() allocates the buffer that receives the STHYI response
block before it is copied to the guest.

This buffer can be allocated with kmalloc() as there's nothing special
about it to go directly to the page allocator.

kmalloc() provides a better API that does not require ugly casts and
kfree() does not need to know the size of the freed object.

Performance difference between kmalloc() and __get_free_pages() is not
measurable as both allocators take an object/page from a per-CPU list for
fast path allocations.

For the slow path the performance is anyway determined by the amount of
reclaim involved rather than by what allocator is used.

Replace use of get_zeroed_page() with kzalloc() and free_page() with
kfree().

Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@xxxxxxxxxx
Assisted-by: copilot:claude-opus
Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
---
 arch/s390/kvm/s390/intercept.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/s390/kvm/s390/intercept.c b/arch/s390/kvm/s390/intercept.c
index ca1205dfac8b0..aaf9828d1f44d 100644
--- a/arch/s390/kvm/s390/intercept.c
+++ b/arch/s390/kvm/s390/intercept.c
@@ -11,6 +11,7 @@
 #include <linux/kvm_host.h>
 #include <linux/errno.h>
 #include <linux/pagemap.h>
+#include <linux/slab.h>
 
 #include <asm/asm-offsets.h>
 #include <asm/irq.h>
@@ -438,13 +439,13 @@ int handle_sthyi(struct kvm_vcpu *vcpu)
 	if (!kvm_s390_pv_cpu_is_protected(vcpu) && (addr & ~PAGE_MASK))
 		return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
 
-	sctns = (void *)get_zeroed_page(GFP_KERNEL_ACCOUNT);
+	sctns = kzalloc(PAGE_SIZE, GFP_KERNEL_ACCOUNT);
 	if (!sctns)
 		return -ENOMEM;
 
 	cc = sthyi_fill(sctns, &rc);
 	if (cc < 0) {
-		free_page((unsigned long)sctns);
+		kfree(sctns);
 		return cc;
 	}
 out:
@@ -454,13 +455,13 @@ int handle_sthyi(struct kvm_vcpu *vcpu)
 		} else {
 			r = write_guest(vcpu, addr, reg2, sctns, PAGE_SIZE);
 			if (r) {
-				free_page((unsigned long)sctns);
+				kfree(sctns);
 				return kvm_s390_inject_prog_cond(vcpu, r);
 			}
 		}
 	}
 
-	free_page((unsigned long)sctns);
+	kfree(sctns);
 	vcpu->run->s.regs.gprs[reg2 + 1] = rc;
 	kvm_s390_set_psw_cc(vcpu, cc);
 	return r;

-- 
2.53.0