linux-kernel - [PATCH gmem] KVM: selftests: Fix gmem conversion tests for multiple vCPUs

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Date:   Mon, 16 Oct 2023 13:47:37 -0500
From:   Michael Roth <michael.roth@....com>
To:     <kvm@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, <seanjc@...gle.com>,
        <pbonzini@...hat.com>, <vannapurve@...gle.com>
Subject: [PATCH gmem] KVM: selftests: Fix gmem conversion tests for multiple vCPUs

Currently the private_mem_conversions_test crashes if invoked with the
-n <num_vcpus> option without also specifying multiple memslots via -m.

This is because the current implementation assumes -m is specified and
always sets up the per-vCPU memory with a dedicated memslot for each
vCPU. When -m is not specified, the test skips setting up
memslots/memory for secondary vCPUs.

The current code does seem to try to handle using a single memslot for
multiple vCPUs in some places, e.g. the call-site, but
test_mem_conversions() is missing the important bit of sizing the single
memslot appropriately to handle all the per-vCPU memory. Implement that
handling.

Signed-off-by: Michael Roth <michael.roth@....com>
---
 .../kvm/x86_64/private_mem_conversions_test.c        | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86_64/private_mem_conversions_test.c b/tools/testing/selftests/kvm/x86_64/private_mem_conversions_test.c
index c04e7d61a585..5eb693fead33 100644
--- a/tools/testing/selftests/kvm/x86_64/private_mem_conversions_test.c
+++ b/tools/testing/selftests/kvm/x86_64/private_mem_conversions_test.c
@@ -388,10 +388,14 @@ static void test_mem_conversions(enum vm_mem_backing_src_type src_type, uint32_t
 		gmem_flags = 0;
 	memfd = vm_create_guest_memfd(vm, memfd_size, gmem_flags);
 
-	for (i = 0; i < nr_memslots; i++)
-		vm_mem_add(vm, src_type, BASE_DATA_GPA + size * i,
-			   BASE_DATA_SLOT + i, size / vm->page_size,
-			   KVM_MEM_PRIVATE, memfd, size * i);
+	if (nr_memslots == 1)
+		vm_mem_add(vm, src_type, BASE_DATA_GPA, BASE_DATA_SLOT,
+			   memfd_size / vm->page_size, KVM_MEM_PRIVATE, memfd, 0);
+	else
+		for (i = 0; i < nr_memslots; i++)
+			vm_mem_add(vm, src_type, BASE_DATA_GPA + size * i,
+				   BASE_DATA_SLOT + i, size / vm->page_size,
+				   KVM_MEM_PRIVATE, memfd, size * i);
 
 	for (i = 0; i < nr_vcpus; i++) {
 		uint64_t gpa =  BASE_DATA_GPA + i * size;
-- 
2.25.1