commit 6d462830e7cf9ce7689986327be3a317f1f990da
author Kevin O'Connor <kevin@koconnor.net> Wed Jan 19 14:08:05 2022 -0500
committer Kevin O'Connor <kevin@koconnor.net> Thu Jan 27 11:26:11 2022 -0500
tree ba4d59fafbf6ee2e6debe1c2c8b4c1a86d799e43
parent f13b650015eba78725ceaf992b5ad6858fd77769

nvme: Only allocate one dma bounce buffer for all nvme drives

There is no need to create multiple dma bounce buffers as the BIOS
disk code isn't reentrant capable.

Also, verify that the allocation succeeds.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
Reviewed-by: Alexander Graf <graf@amazon.com>

src/hw/nvme-int.h

diff --git a/src/hw/nvme-int.h b/src/hw/nvme-int.h
index f0d717d..f9c807e 100644
--- a/src/hw/nvme-int.h
+++ b/src/hw/nvme-int.h
@@ -117,9 +117,6 @@
     u32 block_size;
     u32 metadata_size;
     u32 max_req_size;
-
-    /* Page aligned buffer of size NVME_PAGE_SIZE. */
-    char *dma_buffer;
 };
 
 /* Data structures for NVMe admin identify commands */

src/hw/nvme.c

diff --git a/src/hw/nvme.c b/src/hw/nvme.c
index e9c449d..3dfa0ce 100644
--- a/src/hw/nvme.c
+++ b/src/hw/nvme.c
@@ -20,6 +20,9 @@
 #include "nvme.h"
 #include "nvme-int.h"
 
+// Page aligned "dma bounce buffer" of size NVME_PAGE_SIZE in high memory
+static void *nvme_dma_buffer;
+
 static void *
 zalloc_page_aligned(struct zone_s *zone, u32 size)
 {
@@ -257,6 +260,14 @@
         goto free_buffer;
     }
 
+    if (!nvme_dma_buffer) {
+        nvme_dma_buffer = zalloc_page_aligned(&ZoneHigh, NVME_PAGE_SIZE);
+        if (!nvme_dma_buffer) {
+            warn_noalloc();
+            goto free_buffer;
+        }
+    }
+
     struct nvme_namespace *ns = malloc_fseg(sizeof(*ns));
     if (!ns) {
         warn_noalloc();
@@ -294,8 +305,6 @@
         ns->max_req_size = -1U;
     }
 
-    ns->dma_buffer = zalloc_page_aligned(&ZoneHigh, NVME_PAGE_SIZE);
-
     char *desc = znprintf(MAXDESCSIZE, "NVMe NS %u: %llu MiB (%llu %u-byte "
                           "blocks + %u-byte metadata)",
                           ns_id, (ns->lba_count * ns->block_size) >> 20,
@@ -459,12 +468,12 @@
     u16 blocks = count < max_blocks ? count : max_blocks;
 
     if (write)
-        memcpy(ns->dma_buffer, buf, blocks * ns->block_size);
+        memcpy(nvme_dma_buffer, buf, blocks * ns->block_size);
 
-    int res = nvme_io_xfer(ns, lba, ns->dma_buffer, NULL, blocks, write);
+    int res = nvme_io_xfer(ns, lba, nvme_dma_buffer, NULL, blocks, write);
 
     if (!write && res >= 0)
-        memcpy(buf, ns->dma_buffer, res * ns->block_size);
+        memcpy(buf, nvme_dma_buffer, res * ns->block_size);
 
     return res;
 }
@@ -498,7 +507,7 @@
     /* Build PRP list if we need to describe more than 2 pages */
     if ((ns->block_size * count) > (NVME_PAGE_SIZE * 2)) {
         u32 prpl_len = 0;
-        u64 *prpl = (void*)ns->dma_buffer;
+        u64 *prpl = nvme_dma_buffer;
         int first_page = 1;
         for (; size > 0; base += NVME_PAGE_SIZE, size -= NVME_PAGE_SIZE) {
             if (first_page) {