virtio: bounce.in_use==true in virtqueue_map_desc()

Host environment

• Operating system: Ubuntu 24.04 (Noble)

• OS/kernel version: Linux 6.5.0-13-generic

• Architecture: amd64

• QEMU flavor: qemu-system-riscv64

• QEMU version: 8.2-rc2 / 8.1.92

• QEMU command line:

  /usr/bin/qemu-system-riscv64 \
         -M virt,acpi=off -accel tcg -m 4096 \
         -serial mon:stdio \
         -device virtio-gpu-pci \
         -device qemu-xhci \
         -device usb-kbd \
         -drive if=pflash,format=raw,unit=0,file=RISCV_VIRT_CODE.fd,readonly=on \
         -drive if=pflash,format=raw,unit=1,file=RISCV_VIRT_VARS.fd \
         -drive file=sct.img,format=raw,if=virtio \
         -device virtio-net-device,netdev=net0 \
         -netdev user,id=net0

Emulated/Virtualized environment

• Operating system: EDK II
• OS/kernel version: edk2-stable202311
• Architecture: riscv64

Description of problem

Steps to reproduce

1. Build EDK II (edk2-stable202311) for riscv64
2. Build UEFI SCT (commit 81dfa8d53d4290) for riscv64
3. Run the UEFI SCT
4. Observe the message "qemu: virtio: bogus descriptor or out of resources" after which the execution stalls.

The full procedure is described in https://github.com/xypron/sct_release_test

To save time you can call sct -u and select only test 'MediaAccessTest\BlockIOProtocolTest'. Run it with F9.

Additional information

virtqueue_map_desc() may be called for a large buffers size sz. It will then call dma_memory_map() multiple times in a loop. In address_space_map() bounce.in_use is set to true on the first call. Each subsequent call is bound to fail.

To verify this is the cause I applied the following diff:

diff --git a/system/physmem.c b/system/physmem.c
index a63853a7bc..12b3c2f828 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -3151,12 +3151,16 @@ void *address_space_map(AddressSpace *as,
 
     if (!memory_access_is_direct(mr, is_write)) {
         if (qatomic_xchg(&bounce.in_use, true)) {
+           fprintf(stderr, "bounce.in_use in address_space_map\n");
+
             *plen = 0;
             return NULL;
         }
         /* Avoid unbounded allocations */
         l = MIN(l, TARGET_PAGE_SIZE);
         bounce.buffer = qemu_memalign(TARGET_PAGE_SIZE, l);
+       if (!bounce.buffer)
+           fprintf(stderr, "Out of memory in address_space_map\n");
         bounce.addr = addr;
         bounce.len = l;

and saw this output:

Logfile: "\sct\Log\MediaAccessTest\BlockIOProtocolTest0\ReadBlocks_Conf_0_0_8261
59D3-04A5-4CCE-8431-344707A8B57A.log"
Test Started: 12/02/23  08:43a
------------------------------------------------------------
Current Device: Acpi(PNP0A03,0)/Pci(3|0)
Bounce.in_use in address_space_map
qemu: virtio: bogus descriptor or out of resources

See related bug #850.