[Qemu-devel] [PATCH] fw_cfg: don't use DMA mapping for fw_cfg device

[Peter Xu]

fw_cfg device does not need IOMMU protection, so use physical addresses
always.  That's how QEMU implements fw_cfg.  Otherwise we'll see call
traces during boot when vIOMMU is enabled in guest:

[    1.018306] ------------[ cut here ]------------
[    1.018314] WARNING: CPU: 1 PID: 1 at drivers/firmware/qemu_fw_cfg.c:152 
fw_cfg_dma_transfer+0x399/0x500
[    1.018315] fw_cfg_dma_transfer: failed to map fw_cfg_dma
[    1.018316] Modules linked in:
[    1.018320] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 3.10.0-827.el7.x86_64 
#1
[    1.018321] Hardware name: Red Hat KVM, BIOS 1.11.0-1.el7 04/01/2014
[    1.018322] Call Trace:
[    1.018330]  [<ffffffffafcf6b3a>] dump_stack+0x19/0x1b
[    1.018334]  [<ffffffffaf68fff8>] __warn+0xd8/0x100
[    1.018336]  [<ffffffffaf69007f>] warn_slowpath_fmt+0x5f/0x80
[    1.018338]  [<ffffffffafb67329>] fw_cfg_dma_transfer+0x399/0x500
[    1.018340]  [<ffffffffafb6753c>] fw_cfg_read_blob+0xac/0x1c0
[    1.018342]  [<ffffffffafb67720>] fw_cfg_register_dir_entries+0x80/0x450
[    1.018344]  [<ffffffffafb67d02>] fw_cfg_sysfs_probe+0x212/0x3f0
[    1.018347]  [<ffffffffafa70352>] platform_drv_probe+0x42/0x110
[    1.018350]  [<ffffffffafa6e002>] driver_probe_device+0xc2/0x3e0
[    1.018352]  [<ffffffffafa6e3f3>] __driver_attach+0x93/0xa0
[    1.018354]  [<ffffffffafa6e360>] ? __device_attach+0x40/0x40
[    1.018359]  [<ffffffffafa6bbd3>] bus_for_each_dev+0x73/0xc0
[    1.018362]  [<ffffffffafa6d97e>] driver_attach+0x1e/0x20
[    1.018364]  [<ffffffffafa6d420>] bus_add_driver+0x200/0x2d0
[    1.018366]  [<ffffffffb03c2041>] ? firmware_map_add_early+0x58/0x58
[    1.018368]  [<ffffffffafa6ea84>] driver_register+0x64/0xf0
[    1.018370]  [<ffffffffafa7013a>] __platform_driver_register+0x4a/0x50
[    1.018372]  [<ffffffffb03c2075>] fw_cfg_sysfs_init+0x34/0x61
[    1.018376]  [<ffffffffaf602108>] do_one_initcall+0xb8/0x230
[    1.018379]  [<ffffffffb036b34a>] kernel_init_freeable+0x17a/0x219
[    1.018381]  [<ffffffffb036ab19>] ? initcall_blacklist+0xb0/0xb0
[    1.018383]  [<ffffffffafce5b30>] ? rest_init+0x80/0x80
[    1.018385]  [<ffffffffafce5b3e>] kernel_init+0xe/0xf0
[    1.018388]  [<ffffffffafd08898>] ret_from_fork+0x58/0x90
[    1.018390]  [<ffffffffafce5b30>] ? rest_init+0x80/0x80
[    1.018392] ---[ end trace d00a5b71608a8f59 ]---

Bug: https://bugzilla.redhat.com/show_bug.cgi?id=1533367
Fixes: e90cb816599b ("fw_cfg: do DMA read operation", 2017-11-28)
CC: Marc-André Lureau <address@hidden>
CC: Michael S. Tsirkin <address@hidden>
Signed-off-by: Peter Xu <address@hidden>
--

This is based on tree:
  https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git/log/?h=vhost

Please review, thanks.

Signed-off-by: Peter Xu <address@hidden>
---
 drivers/firmware/qemu_fw_cfg.c | 37 ++++++++-----------------------------
 1 file changed, 8 insertions(+), 29 deletions(-)

diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
index 6eb5d8f43c3e..62a44bc81a88 100644
--- a/drivers/firmware/qemu_fw_cfg.c
+++ b/drivers/firmware/qemu_fw_cfg.c
@@ -106,11 +106,12 @@ static inline bool fw_cfg_dma_enabled(void)
 }
 
 /* qemu fw_cfg device is sync today, but spec says it may become async */
-static void fw_cfg_wait_for_control(struct fw_cfg_dma *d, dma_addr_t dma)
+static void fw_cfg_wait_for_control(struct fw_cfg_dma *d)
 {
        do {
-               dma_sync_single_for_cpu(dev, dma, sizeof(*d), DMA_FROM_DEVICE);
-               if ((be32_to_cpu(d->control) & ~FW_CFG_DMA_CTL_ERROR) == 0)
+               u32 ctrl = be32_to_cpu(READ_ONCE(d->control));
+
+               if ((ctrl & ~FW_CFG_DMA_CTL_ERROR) == 0)
                        return;
 
                usleep_range(50, 100);
@@ -119,21 +120,9 @@ static void fw_cfg_wait_for_control(struct fw_cfg_dma *d, 
dma_addr_t dma)
 
 static ssize_t fw_cfg_dma_transfer(void *address, u32 length, u32 control)
 {
-       dma_addr_t dma_addr = 0;
        struct fw_cfg_dma *d = NULL;
-       dma_addr_t dma;
        ssize_t ret = length;
-       enum dma_data_direction dir =
-               (control & FW_CFG_DMA_CTL_READ ? DMA_FROM_DEVICE : 0) |
-               (control & FW_CFG_DMA_CTL_WRITE ? DMA_TO_DEVICE : 0);
-
-       if (address && length) {
-               dma_addr = dma_map_single(dev, address, length, dir);
-               if (dma_mapping_error(NULL, dma_addr)) {
-                       WARN(1, "%s: failed to map address\n", __func__);
-                       return -EFAULT;
-               }
-       }
+       phys_addr_t dma;
 
        d = kmalloc(sizeof(*d), GFP_KERNEL);
        if (!d) {
@@ -142,34 +131,24 @@ static ssize_t fw_cfg_dma_transfer(void *address, u32 
length, u32 control)
        }
 
        *d = (struct fw_cfg_dma) {
-               .address = cpu_to_be64(dma_addr),
+               .address = cpu_to_be64(virt_to_phys(address)),
                .length = cpu_to_be32(length),
                .control = cpu_to_be32(control)
        };
 
-       dma = dma_map_single(dev, d, sizeof(*d), DMA_BIDIRECTIONAL);
-       if (dma_mapping_error(NULL, dma)) {
-               WARN(1, "%s: failed to map fw_cfg_dma\n", __func__);
-               ret = -EFAULT;
-               goto end;
-       }
+       dma = virt_to_phys(d);
 
        iowrite32be((u64)dma >> 32, fw_cfg_reg_dma);
        iowrite32be(dma, fw_cfg_reg_dma + 4);
 
-       fw_cfg_wait_for_control(d, dma);
+       fw_cfg_wait_for_control(d);
 
        if (be32_to_cpu(d->control) & FW_CFG_DMA_CTL_ERROR) {
                ret = -EIO;
        }
 
-       dma_unmap_single(dev, dma, sizeof(*d), DMA_BIDIRECTIONAL);
-
 end:
        kfree(d);
-       if (dma_addr)
-               dma_unmap_single(dev, dma_addr, length, dir);
-
        return ret;
 }
 
-- 
2.14.3