handle_stsi() allocates the buffer that receives the STSI 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.

While on it, make the buffer a void pointer to get rid of the casts.

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

Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com
Assisted-by: copilot:claude-opus
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 arch/s390/kvm/s390/priv.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/arch/s390/kvm/s390/priv.c b/arch/s390/kvm/s390/priv.c
index b3cb2c2c3aa71..856939acf012f 100644
--- a/arch/s390/kvm/s390/priv.c
+++ b/arch/s390/kvm/s390/priv.c
@@ -14,6 +14,7 @@
 #include <linux/mm_types.h>
 #include <linux/pgtable.h>
 #include <linux/io.h>
+#include <linux/slab.h>
 #include <asm/asm-offsets.h>
 #include <asm/facility.h>
 #include <asm/current.h>
@@ -869,7 +870,7 @@ static int handle_stsi(struct kvm_vcpu *vcpu)
 	int fc = (vcpu->run->s.regs.gprs[0] & 0xf0000000) >> 28;
 	int sel1 = vcpu->run->s.regs.gprs[0] & 0xff;
 	int sel2 = vcpu->run->s.regs.gprs[1] & 0xffff;
-	unsigned long mem = 0;
+	void *mem = NULL;
 	u64 operand2;
 	int rc = 0;
 	u8 ar;
@@ -911,19 +912,19 @@ static int handle_stsi(struct kvm_vcpu *vcpu)
 	switch (fc) {
 	case 1: /* same handling for 1 and 2 */
 	case 2:
-		mem = get_zeroed_page(GFP_KERNEL_ACCOUNT);
+		mem = kzalloc(PAGE_SIZE, GFP_KERNEL_ACCOUNT);
 		if (!mem)
 			goto out_no_data;
-		if (stsi((void *) mem, fc, sel1, sel2))
+		if (stsi(mem, fc, sel1, sel2))
 			goto out_no_data;
 		break;
 	case 3:
 		if (sel1 != 2 || sel2 != 2)
 			goto out_no_data;
-		mem = get_zeroed_page(GFP_KERNEL_ACCOUNT);
+		mem = kzalloc(PAGE_SIZE, GFP_KERNEL_ACCOUNT);
 		if (!mem)
 			goto out_no_data;
-		handle_stsi_3_2_2(vcpu, (void *) mem);
+		handle_stsi_3_2_2(vcpu, mem);
 		break;
 	case 15: /* fc 15 is fully handled in userspace */
 		insert_stsi_usr_data(vcpu, operand2, ar, fc, sel1, sel2);
@@ -931,10 +932,10 @@ static int handle_stsi(struct kvm_vcpu *vcpu)
 		return -EREMOTE;
 	}
 	if (kvm_s390_pv_cpu_is_protected(vcpu)) {
-		memcpy(sida_addr(vcpu->arch.sie_block), (void *)mem, PAGE_SIZE);
+		memcpy(sida_addr(vcpu->arch.sie_block), mem, PAGE_SIZE);
 		rc = 0;
 	} else {
-		rc = write_guest(vcpu, operand2, ar, (void *)mem, PAGE_SIZE);
+		rc = write_guest(vcpu, operand2, ar, mem, PAGE_SIZE);
 	}
 	if (rc) {
 		rc = kvm_s390_inject_prog_cond(vcpu, rc);
@@ -945,14 +946,14 @@ static int handle_stsi(struct kvm_vcpu *vcpu)
 		rc = -EREMOTE;
 	}
 	trace_kvm_s390_handle_stsi(vcpu, fc, sel1, sel2, operand2);
-	free_page(mem);
+	kfree(mem);
 	kvm_s390_set_psw_cc(vcpu, 0);
 	vcpu->run->s.regs.gprs[0] = 0;
 	return rc;
 out_no_data:
 	kvm_s390_set_psw_cc(vcpu, 3);
 out:
-	free_page(mem);
+	kfree(mem);
 	return rc;
 }
 

-- 
2.53.0