linux-kernel - [RFC PATCH v2 11/51] KVM: selftests: Allow cleanup of ucall

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Message-ID: <09e75529c3f844b1bb4dd5a096ed4160905fca7f.1747264138.git.ackerleytng@google.com>
Date: Wed, 14 May 2025 16:41:50 -0700
From: Ackerley Tng <ackerleytng@...gle.com>
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Subject: [RFC PATCH v2 11/51] KVM: selftests: Allow cleanup of ucall_pool from host

Many selftests use GUEST_DONE() to signal the end of guest code, which
is handled in userspace. In most tests, the test exits and there is no
need to clean up the ucall_pool->in_use bitmap.

If there are many guest code functions using GUEST_DONE(), or of guest
code functions are run many times, the ucall_pool->in_use bitmap will
fill up, causing later runs of the same guest code function to fail.

This patch allows ucall_free() to be called from userspace on uc.hva,
which will unset and free the correct struct ucall in the pool,
allowing ucalls to continue being used.

Change-Id: I2cb2aeed4b291b1bfb2bece001d09c509cd10446
Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
---
 .../testing/selftests/kvm/include/ucall_common.h |  1 +
 tools/testing/selftests/kvm/lib/ucall_common.c   | 16 ++++++++--------
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/ucall_common.h b/tools/testing/selftests/kvm/include/ucall_common.h
index d9d6581b8d4f..b6b850d0319a 100644
--- a/tools/testing/selftests/kvm/include/ucall_common.h
+++ b/tools/testing/selftests/kvm/include/ucall_common.h
@@ -40,6 +40,7 @@ __printf(5, 6) void ucall_assert(uint64_t cmd, const char *exp,
 				 const char *fmt, ...);
 uint64_t get_ucall(struct kvm_vcpu *vcpu, struct ucall *uc);
 void ucall_init(struct kvm_vm *vm, vm_paddr_t mmio_gpa);
+void ucall_free(struct ucall *uc);
 int ucall_nr_pages_required(uint64_t page_size);
 
 /*
diff --git a/tools/testing/selftests/kvm/lib/ucall_common.c b/tools/testing/selftests/kvm/lib/ucall_common.c
index 42151e571953..9b6865c39ea7 100644
--- a/tools/testing/selftests/kvm/lib/ucall_common.c
+++ b/tools/testing/selftests/kvm/lib/ucall_common.c
@@ -21,24 +21,24 @@ int ucall_nr_pages_required(uint64_t page_size)
 
 /*
  * ucall_pool holds per-VM values (global data is duplicated by each VM), it
- * must not be accessed from host code.
+ * should generally not be accessed from host code other than via ucall_free(),
+ * to cleanup after using GUEST_DONE()
  */
 static struct ucall_header *ucall_pool;
 
 void ucall_init(struct kvm_vm *vm, vm_paddr_t mmio_gpa)
 {
-	struct ucall_header *hdr;
 	struct ucall *uc;
 	vm_vaddr_t vaddr;
 	int i;
 
-	vaddr = vm_vaddr_alloc_shared(vm, sizeof(*hdr), KVM_UTIL_MIN_VADDR,
-				      MEM_REGION_DATA);
-	hdr = (struct ucall_header *)addr_gva2hva(vm, vaddr);
-	memset(hdr, 0, sizeof(*hdr));
+	vaddr = vm_vaddr_alloc_shared(vm, sizeof(*ucall_pool),
+				      KVM_UTIL_MIN_VADDR, MEM_REGION_DATA);
+	ucall_pool = (struct ucall_header *)addr_gva2hva(vm, vaddr);
+	memset(ucall_pool, 0, sizeof(*ucall_pool));
 
 	for (i = 0; i < KVM_MAX_VCPUS; ++i) {
-		uc = &hdr->ucalls[i];
+		uc = &ucall_pool->ucalls[i];
 		uc->hva = uc;
 	}
 
@@ -73,7 +73,7 @@ static struct ucall *ucall_alloc(void)
 	return NULL;
 }
 
-static void ucall_free(struct ucall *uc)
+void ucall_free(struct ucall *uc)
 {
 	/* Beware, here be pointer arithmetic.  */
 	clear_bit(uc - ucall_pool->ucalls, ucall_pool->in_use);
-- 
2.49.0.1045.g170613ef41-goog