With -kernel/-initrd, x86_load_linux() places the initrd at the top
of low RAM but does not reserve that range in e820. SeaBIOS
allocates virtio vrings top-down from the same area, so with enough
devices the vrings overlap the initrd and firmware DMA corrupts it.
Reserve the initrd range in the e820 table; SeaBIOS and OVMF both
honor "etc/e820" reservations when setting up their memory
allocators.
Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4396
Signed-off-by: Ray Lee <hburaylee@gmail.com>
---
hw/i386/x86-common.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/hw/i386/x86-common.c b/hw/i386/x86-common.c
index 8f9419e7d3..4e85fde987 100644
--- a/hw/i386/x86-common.c
+++ b/hw/i386/x86-common.c
@@ -38,6 +38,7 @@
#include "hw/core/irq.h"
#include "hw/core/loader.h"
+#include "e820_memory_layout.h"
#include "multiboot.h"
#include "elf.h"
#include "standard-headers/asm-x86/bootparam.h"
@@ -744,6 +745,13 @@ void x86_load_linux(X86MachineState *x86ms,
initrd_addr = (initrd_max - initrd_size) & ~4095;
+ /*
+ * Keep firmware (e.g. SeaBIOS) from allocating over the
+ * initrd at the top of RAM.
+ */
+ e820_add_entry(initrd_addr, QEMU_ALIGN_UP(initrd_size, 4096),
+ E820_RESERVED);
+
fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_ADDR, initrd_addr);
fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_SIZE, initrd_size);
fw_cfg_add_bytes(fw_cfg, FW_CFG_INITRD_DATA, initrd_data,
@@ -889,6 +897,13 @@ void x86_load_linux(X86MachineState *x86ms,
initrd_addr = (initrd_max - initrd_size) & ~4095;
+ /*
+ * Keep firmware (e.g. SeaBIOS) from allocating over the initrd
+ * at the top of RAM.
+ */
+ e820_add_entry(initrd_addr, QEMU_ALIGN_UP(initrd_size, 4096),
+ E820_RESERVED);
+
fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_ADDR, initrd_addr);
fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_SIZE, initrd_size);
fw_cfg_add_bytes(fw_cfg, FW_CFG_INITRD_DATA, initrd_data, initrd_size);
--
2.53.0