[PATCH-for-5.2 v2 23/25] block/nvme: Fix use of write-only doorbells page on Aarch64 arch

[Philippe Mathieu-Daudé]

qemu_vfio_pci_map_bar() calls mmap(), and mmap(2) states:

  'offset' must be a multiple of the page size as returned
   by sysconf(_SC_PAGE_SIZE).

In commit f68453237b9 we started to use an offset of 4K which
broke this contract on Aarch64 arch.

Fix by mapping at offset 0, and and accessing doorbells at offset=4K.

Fixes: f68453237b9 ("block/nvme: Map doorbells pages write-only")
Reported-by: Eric Auger <eric.au...@redhat.com>
Reviewed-by: Eric Auger <eric.au...@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
Tested-by: Eric Auger <eric.au...@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <phi...@redhat.com>
---
 block/nvme.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/block/nvme.c b/block/nvme.c
index f1e2fd34cdf..c8ef69cbb28 100644
--- a/block/nvme.c
+++ b/block/nvme.c
@@ -94,6 +94,7 @@ typedef struct {
 struct BDRVNVMeState {
     AioContext *aio_context;
     QEMUVFIOState *vfio;
+    void *bar0_wo_map;
     /* Memory mapped registers */
     volatile struct {
         uint32_t sq_tail;
@@ -777,8 +778,10 @@ static int nvme_init(BlockDriverState *bs, const char 
*device, int namespace,
         }
     }
 
-    s->doorbells = qemu_vfio_pci_map_bar(s->vfio, 0, sizeof(NvmeBar),
-                                         NVME_DOORBELL_SIZE, PROT_WRITE, errp);
+    s->bar0_wo_map = qemu_vfio_pci_map_bar(s->vfio, 0, 0,
+                                           sizeof(NvmeBar) + 
NVME_DOORBELL_SIZE,
+                                           PROT_WRITE, errp);
+    s->doorbells = (void *)((uintptr_t)s->bar0_wo_map + sizeof(NvmeBar));
     if (!s->doorbells) {
         ret = -EINVAL;
         goto out;
@@ -910,8 +913,8 @@ static void nvme_close(BlockDriverState *bs)
                            &s->irq_notifier[MSIX_SHARED_IRQ_IDX],
                            false, NULL, NULL);
     event_notifier_cleanup(&s->irq_notifier[MSIX_SHARED_IRQ_IDX]);
-    qemu_vfio_pci_unmap_bar(s->vfio, 0, (void *)s->doorbells,
-                            sizeof(NvmeBar), NVME_DOORBELL_SIZE);
+    qemu_vfio_pci_unmap_bar(s->vfio, 0, s->bar0_wo_map,
+                            0, sizeof(NvmeBar) + NVME_DOORBELL_SIZE);
     qemu_vfio_close(s->vfio);
 
     g_free(s->device);
-- 
2.26.2