selftests/ublk: add read-only buffer registration test

Add --rdonly_shmem_buf option to kublk that registers shared memory
buffers with UBLK_SHMEM_BUF_READ_ONLY (read-only pinning without
FOLL_WRITE) and mmaps with PROT_READ only.

Add test_shmemzc_04.sh which exercises the new flag with a null target,
hugetlbfs buffer, and write workload. Write I/O works because the
server only reads from the shared buffer — the data flows from client
to kernel to the shared pages, and the server reads them out.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://patch.msgid.link/20260331153207.3635125-11-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/tools/testing/selftests/ublk/Makefile b/tools/testing/selftests/ublk/Makefile
index c453cd3690880c1fb298c5c639a567e875c17099..ec6a8ce83d38123fc1ef51660254ed46e085b531 100644 (file)
--- a/tools/testing/selftests/ublk/Makefile
+++ b/tools/testing/selftests/ublk/Makefile
@@ -55,6 +55,7 @@ TEST_PROGS += test_part_02.sh
 TEST_PROGS += test_shmemzc_01.sh
 TEST_PROGS += test_shmemzc_02.sh
 TEST_PROGS += test_shmemzc_03.sh
+TEST_PROGS += test_shmemzc_04.sh
 
 TEST_PROGS += test_stress_01.sh
 TEST_PROGS += test_stress_02.sh

diff --git a/tools/testing/selftests/ublk/kublk.c b/tools/testing/selftests/ublk/kublk.c
index fce3f80c3ebacd4f4af1f7a8a399a8fc9a8989e7..fbd9b1e7342a3550d2cf5c8036c15f9e91279b6f 100644 (file)
--- a/tools/testing/selftests/ublk/kublk.c
+++ b/tools/testing/selftests/ublk/kublk.c
@@ -1219,11 +1219,13 @@ static void ublk_shmem_unregister_all(void)
        shmem_count = 0;
 }
 
-static int ublk_ctrl_reg_buf(struct ublk_dev *dev, void *addr, size_t size)
+static int ublk_ctrl_reg_buf(struct ublk_dev *dev, void *addr, size_t size,
+                            __u32 flags)
 {
        struct ublk_shmem_buf_reg buf_reg = {
                .addr = (unsigned long)addr,
                .len = size,
+               .flags = flags,
        };
        struct ublk_ctrl_cmd_data data = {
                .cmd_op = UBLK_U_CMD_REG_BUF,
@@ -1272,7 +1274,7 @@ static void ublk_shmem_handle_client(int sock_fd, struct ublk_dev *dev)
        }
 
        /* Register server's VA range with kernel for PFN matching */
-       ret = ublk_ctrl_reg_buf(dev, base, size);
+       ret = ublk_ctrl_reg_buf(dev, base, size, 0);
        if (ret < 0) {
                ublk_dbg(UBLK_DBG_DEV,
                         "shmem_zc: kernel reg failed %d\n", ret);
@@ -1357,7 +1359,8 @@ static int ublk_shmem_htlb_setup(const struct dev_ctx *ctx,
                return -EINVAL;
        }
 
-       base = mmap(NULL, st.st_size, PROT_READ | PROT_WRITE,
+       base = mmap(NULL, st.st_size,
+                   ctx->rdonly_shmem_buf ? PROT_READ : PROT_READ | PROT_WRITE,
                    MAP_SHARED | MAP_POPULATE, fd, 0);
        if (base == MAP_FAILED) {
                ublk_err("htlb: mmap failed\n");
@@ -1365,7 +1368,8 @@ static int ublk_shmem_htlb_setup(const struct dev_ctx *ctx,
                return -ENOMEM;
        }
 
-       ret = ublk_ctrl_reg_buf(dev, base, st.st_size);
+       ret = ublk_ctrl_reg_buf(dev, base, st.st_size,
+                              ctx->rdonly_shmem_buf ? UBLK_SHMEM_BUF_READ_ONLY : 0);
        if (ret < 0) {
                ublk_err("htlb: reg_buf failed: %d\n", ret);
                munmap(base, st.st_size);
@@ -2129,6 +2133,7 @@ int main(int argc, char *argv[])
                { "no_auto_part_scan",  0,      NULL,  0 },
                { "shmem_zc",           0,      NULL,  0  },
                { "htlb",               1,      NULL,  0  },
+               { "rdonly_shmem_buf",   0,      NULL,  0  },
                { 0, 0, 0, 0 }
        };
        const struct ublk_tgt_ops *ops = NULL;
@@ -2248,6 +2253,8 @@ int main(int argc, char *argv[])
                                ctx.flags |= UBLK_F_SHMEM_ZC;
                        if (!strcmp(longopts[option_idx].name, "htlb"))
                                ctx.htlb_path = strdup(optarg);
+                       if (!strcmp(longopts[option_idx].name, "rdonly_shmem_buf"))
+                               ctx.rdonly_shmem_buf = 1;
                        break;
                case '?':
                        /*

diff --git a/tools/testing/selftests/ublk/kublk.h b/tools/testing/selftests/ublk/kublk.h
index 8ed2efc3ecb99ca634d70729203430ae61d8db82..742c41d77df143645a2b02430e2a57088534d66c 100644 (file)
--- a/tools/testing/selftests/ublk/kublk.h
+++ b/tools/testing/selftests/ublk/kublk.h
@@ -81,6 +81,7 @@ struct dev_ctx {
        unsigned int    no_ublk_fixed_fd:1;
        unsigned int    safe_stop:1;
        unsigned int    no_auto_part_scan:1;
+       unsigned int    rdonly_shmem_buf:1;
        __u32 integrity_flags;
        __u8 metadata_size;
        __u8 pi_offset;

diff --git a/tools/testing/selftests/ublk/test_shmemzc_04.sh b/tools/testing/selftests/ublk/test_shmemzc_04.sh
new file mode 100755 (executable)
index 0000000..899de08
--- /dev/null
+++ b/tools/testing/selftests/ublk/test_shmemzc_04.sh
@@ -0,0 +1,72 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Test: shmem_zc with read-only buffer registration on null target
+#
+# Same as test_shmemzc_01 but with --rdonly_shmem_buf: pages are pinned
+# without FOLL_WRITE (UBLK_BUF_F_READ).  Write I/O works because
+# the server only reads from the shared buffer.
+
+. "$(cd "$(dirname "$0")" && pwd)"/test_common.sh
+
+ERR_CODE=0
+
+_prep_test "shmem_zc" "null target hugetlbfs shmem zero-copy rdonly_buf test"
+
+if ! _have_program fio; then
+       echo "SKIP: fio not available"
+       exit "$UBLK_SKIP_CODE"
+fi
+
+if ! grep -q hugetlbfs /proc/filesystems; then
+       echo "SKIP: hugetlbfs not supported"
+       exit "$UBLK_SKIP_CODE"
+fi
+
+# Allocate hugepages
+OLD_NR_HP=$(cat /proc/sys/vm/nr_hugepages)
+echo 10 > /proc/sys/vm/nr_hugepages
+NR_HP=$(cat /proc/sys/vm/nr_hugepages)
+if [ "$NR_HP" -lt 2 ]; then
+       echo "SKIP: cannot allocate hugepages"
+       echo "$OLD_NR_HP" > /proc/sys/vm/nr_hugepages
+       exit "$UBLK_SKIP_CODE"
+fi
+
+# Mount hugetlbfs
+HTLB_MNT=$(mktemp -d "${UBLK_TEST_DIR}/htlb_mnt_XXXXXX")
+if ! mount -t hugetlbfs none "$HTLB_MNT"; then
+       echo "SKIP: cannot mount hugetlbfs"
+       rmdir "$HTLB_MNT"
+       echo "$OLD_NR_HP" > /proc/sys/vm/nr_hugepages
+       exit "$UBLK_SKIP_CODE"
+fi
+
+HTLB_FILE="$HTLB_MNT/ublk_buf"
+fallocate -l 4M "$HTLB_FILE"
+
+dev_id=$(_add_ublk_dev -t null --shmem_zc --htlb "$HTLB_FILE" --rdonly_shmem_buf)
+_check_add_dev $TID $?
+
+fio --name=htlb_zc_rdonly \
+       --filename=/dev/ublkb"${dev_id}" \
+       --ioengine=io_uring \
+       --rw=randwrite \
+       --direct=1 \
+       --bs=4k \
+       --size=4M \
+       --iodepth=32 \
+       --mem=mmaphuge:"$HTLB_FILE" \
+       > /dev/null 2>&1
+ERR_CODE=$?
+
+# Delete device first so daemon releases the htlb mmap
+_ublk_del_dev "${dev_id}"
+
+rm -f "$HTLB_FILE"
+umount "$HTLB_MNT"
+rmdir "$HTLB_MNT"
+echo "$OLD_NR_HP" > /proc/sys/vm/nr_hugepages
+
+_cleanup_test "shmem_zc"
+
+_show_result $TID $ERR_CODE