* [PATCH v6 1/3] hw/uefi: add query-firmware-log monitor command
2025-10-17 11:50 [PATCH v6 0/3] hw/uefi: add support for receiving the firmware log via monitor Gerd Hoffmann
@ 2025-10-17 11:50 ` Gerd Hoffmann
2025-10-22 5:55 ` Markus Armbruster
2025-10-17 11:50 ` [PATCH v6 2/3] hw/uefi: add 'info firmware-log' hmp " Gerd Hoffmann
2025-10-17 11:50 ` [PATCH v6 3/3] hw/uefi/ovmf-log: add maxsize parameter Gerd Hoffmann
2 siblings, 1 reply; 6+ messages in thread
From: Gerd Hoffmann @ 2025-10-17 11:50 UTC (permalink / raw)
To: qemu-devel
Cc: Eric Blake, Marcel Apfelbaum, Eduardo Habkost, Zhao Liu,
Laurent Vivier, Philippe Mathieu-Daudé, Gerd Hoffmann,
Paolo Bonzini, Fabiano Rosas, Dr. David Alan Gilbert, Yanan Wang,
Markus Armbruster
Starting with the edk2-stable202508 tag OVMF (and ArmVirt too) have
optional support for logging to a memory buffer. There is guest side
support -- for example in linux kernels v6.17+ -- to read that buffer.
But that might not helpful if your guest stops booting early enough that
guest tooling can not be used yet. So host side support to read that
log buffer is a useful thing to have.
This patch implements the query-firmware-log qmp monitor command to
read the firmware log.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
hw/uefi/ovmf-log.c | 233 +++++++++++++++++++++++++++++++++++++
tests/qtest/qmp-cmd-test.c | 2 +
hw/uefi/meson.build | 2 +-
qapi/machine.json | 24 ++++
4 files changed, 260 insertions(+), 1 deletion(-)
create mode 100644 hw/uefi/ovmf-log.c
diff --git a/hw/uefi/ovmf-log.c b/hw/uefi/ovmf-log.c
new file mode 100644
index 000000000000..0d4bd503a06a
--- /dev/null
+++ b/hw/uefi/ovmf-log.c
@@ -0,0 +1,233 @@
+/*
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ * print ovmf debug log
+ *
+ * see OvmfPkg/Library/MemDebugLogLib/ in edk2
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/units.h"
+#include "qemu/target-info-qapi.h"
+#include "hw/boards.h"
+#include "hw/i386/x86.h"
+#include "hw/arm/virt.h"
+#include "system/dma.h"
+#include "monitor/hmp.h"
+#include "monitor/monitor.h"
+#include "qapi/error.h"
+#include "qapi/type-helpers.h"
+#include "qapi/qapi-commands-machine.h"
+
+
+/* ----------------------------------------------------------------------- */
+/* copy from edk2 */
+
+#define MEM_DEBUG_LOG_MAGIC1 0x3167646d666d766f /* "ovmfmdg1" */
+#define MEM_DEBUG_LOG_MAGIC2 0x3267646d666d766f /* "ovmfmdg2" */
+
+/*
+ * Mem Debug Log buffer header.
+ * The Log buffer is circular. Only the most
+ * recent messages are retained. Older messages
+ * will be discarded if the buffer overflows.
+ * The Debug Log starts just after the header.
+ */
+typedef struct {
+ /*
+ * Magic values
+ * These fields are used by tools to locate the buffer in
+ * memory. These MUST be the first two fields of the structure.
+ * Use a 128 bit Magic to vastly reduce the possibility of
+ * a collision with random data in memory.
+ */
+ uint64_t Magic1;
+ uint64_t Magic2;
+ /*
+ * Header Size
+ * This MUST be the third field of the structure
+ */
+ uint64_t HeaderSize;
+ /*
+ * Debug log size (minus header)
+ */
+ uint64_t DebugLogSize;
+ /*
+ * edk2 uses this for locking access.
+ */
+ uint64_t MemDebugLogLock;
+ /*
+ * Debug log head offset
+ */
+ uint64_t DebugLogHeadOffset;
+ /*
+ * Debug log tail offset
+ */
+ uint64_t DebugLogTailOffset;
+ /*
+ * Flag to indicate if the buffer wrapped and was thus truncated.
+ */
+ uint64_t Truncated;
+ /*
+ * Firmware Build Version (PcdFirmwareVersionString)
+ */
+ char FirmwareVersion[128];
+} MEM_DEBUG_LOG_HDR;
+
+
+/* ----------------------------------------------------------------------- */
+/* qemu monitor command */
+
+typedef struct {
+ uint64_t magic1;
+ uint64_t magic2;
+} MemDebugLogMagic;
+
+/* find log buffer in guest memory by searching for the magic cookie */
+static dma_addr_t find_ovmf_log_range(dma_addr_t start, dma_addr_t end)
+{
+ static const MemDebugLogMagic magic = {
+ .magic1 = MEM_DEBUG_LOG_MAGIC1,
+ .magic2 = MEM_DEBUG_LOG_MAGIC2,
+ };
+ MemDebugLogMagic check;
+ dma_addr_t step = 4 * KiB;
+ dma_addr_t offset;
+
+ for (offset = start; offset < end; offset += step) {
+ if (dma_memory_read(&address_space_memory, offset,
+ &check, sizeof(check),
+ MEMTXATTRS_UNSPECIFIED)) {
+ /* dma error -> stop searching */
+ break;
+ }
+ if (memcmp(&magic, &check, sizeof(check)) == 0) {
+ return offset;
+ }
+ }
+ return (dma_addr_t)-1;
+}
+
+static dma_addr_t find_ovmf_log(void)
+{
+ MachineState *ms = MACHINE(qdev_get_machine());
+ dma_addr_t start, end, offset;
+
+ if (target_arch() == SYS_EMU_TARGET_X86_64 &&
+ object_dynamic_cast(OBJECT(ms), TYPE_X86_MACHINE)) {
+ X86MachineState *x86ms = X86_MACHINE(ms);
+
+ /* early log buffer, static allocation in memfd, sec + early pei */
+ offset = find_ovmf_log_range(0x800000, 0x900000);
+ if (offset != -1) {
+ return offset;
+ }
+
+ /*
+ * normal log buffer, dynamically allocated close to end of low memory,
+ * late pei + dxe phase
+ */
+ end = x86ms->below_4g_mem_size;
+ start = end - MIN(end, 128 * MiB);
+ return find_ovmf_log_range(start, end);
+ }
+
+ if (target_arch() == SYS_EMU_TARGET_AARCH64 &&
+ object_dynamic_cast(OBJECT(ms), TYPE_VIRT_MACHINE)) {
+ VirtMachineState *vms = VIRT_MACHINE(ms);
+
+ /* edk2 ArmVirt firmware allocations are in the first 128 MB */
+ start = vms->memmap[VIRT_MEM].base;
+ end = start + 128 * MiB;
+ return find_ovmf_log_range(start, end);
+ }
+
+ return (dma_addr_t)-1;
+}
+
+static void handle_ovmf_log_range(GString *out,
+ dma_addr_t start,
+ dma_addr_t end,
+ Error **errp)
+{
+ if (start > end) {
+ return;
+ }
+
+ size_t len = end - start;
+ g_string_set_size(out, out->len + len);
+ if (dma_memory_read(&address_space_memory, start,
+ out->str + (out->len - len),
+ len, MEMTXATTRS_UNSPECIFIED)) {
+ error_setg(errp, "can not read firmware log buffer contents");
+ return;
+ }
+}
+
+FirmwareLog *qmp_query_firmware_log(Error **errp)
+{
+ MEM_DEBUG_LOG_HDR header;
+ dma_addr_t offset, base;
+ FirmwareLog *ret;
+ g_autoptr(GString) log = g_string_new("");
+
+ offset = find_ovmf_log();
+ if (offset == -1) {
+ error_setg(errp, "firmware log buffer not found");
+ return NULL;
+ }
+
+ if (dma_memory_read(&address_space_memory, offset,
+ &header, sizeof(header),
+ MEMTXATTRS_UNSPECIFIED)) {
+ error_setg(errp, "can not read firmware log buffer header");
+ return NULL;
+ }
+
+ if (header.DebugLogSize > MiB) {
+ /* default size is 128k (32 pages), allow up to 1M */
+ error_setg(errp, "firmware log: log buffer is too big");
+ return NULL;
+ }
+
+ if (header.DebugLogHeadOffset > header.DebugLogSize ||
+ header.DebugLogTailOffset > header.DebugLogSize) {
+ error_setg(errp, "firmware log buffer header is invalid");
+ return NULL;
+ }
+
+ base = offset + header.HeaderSize;
+ if (header.DebugLogHeadOffset > header.DebugLogTailOffset) {
+ /* wrap around */
+ handle_ovmf_log_range(log,
+ base + header.DebugLogHeadOffset,
+ base + header.DebugLogSize,
+ errp);
+ if (*errp) {
+ return NULL;
+ }
+ handle_ovmf_log_range(log,
+ base + 0,
+ base + header.DebugLogTailOffset,
+ errp);
+ if (*errp) {
+ return NULL;
+ }
+ } else {
+ handle_ovmf_log_range(log,
+ base + header.DebugLogHeadOffset,
+ base + header.DebugLogTailOffset,
+ errp);
+ if (*errp) {
+ return NULL;
+ }
+ }
+
+ ret = g_new0(FirmwareLog, 1);
+ if (header.FirmwareVersion[0] != '\0') {
+ ret->version = g_strndup(header.FirmwareVersion,
+ sizeof(header.FirmwareVersion));
+ }
+ ret->log = g_base64_encode((const guchar *)log->str, log->len);
+ return ret;
+}
diff --git a/tests/qtest/qmp-cmd-test.c b/tests/qtest/qmp-cmd-test.c
index cf718761861d..279a8f5614e9 100644
--- a/tests/qtest/qmp-cmd-test.c
+++ b/tests/qtest/qmp-cmd-test.c
@@ -52,6 +52,8 @@ static int query_error_class(const char *cmd)
/* Only valid with accel=tcg */
{ "x-query-jit", ERROR_CLASS_GENERIC_ERROR },
{ "xen-event-list", ERROR_CLASS_GENERIC_ERROR },
+ /* requires firmware with memory buffer logging support */
+ { "query-firmware-log", ERROR_CLASS_GENERIC_ERROR },
{ NULL, -1 }
};
int i;
diff --git a/hw/uefi/meson.build b/hw/uefi/meson.build
index 91eb95f89e6d..c8f38dfae247 100644
--- a/hw/uefi/meson.build
+++ b/hw/uefi/meson.build
@@ -1,4 +1,4 @@
-system_ss.add(files('hardware-info.c'))
+system_ss.add(files('hardware-info.c', 'ovmf-log.c'))
uefi_vars_ss = ss.source_set()
if (config_all_devices.has_key('CONFIG_UEFI_VARS'))
diff --git a/qapi/machine.json b/qapi/machine.json
index 038eab281c78..96133e5c71cf 100644
--- a/qapi/machine.json
+++ b/qapi/machine.json
@@ -1839,6 +1839,30 @@
'returns': 'HumanReadableText',
'features': [ 'unstable' ]}
+##
+# @FirmwareLog:
+#
+# @version: Firmware version.
+#
+# @log: Firmware debug log, in base64 encoding. First and last log
+# line might be incomplete.
+#
+# Since: 10.2
+##
+{ 'struct': 'FirmwareLog',
+ 'data': { '*version': 'str',
+ 'log': 'str' } }
+
+##
+# @query-firmware-log:
+#
+# Find firmware memory log buffer in guest memory, return content.
+#
+# Since: 10.2
+##
+{ 'command': 'query-firmware-log',
+ 'returns': 'FirmwareLog' }
+
##
# @dump-skeys:
#
--
2.51.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH v6 1/3] hw/uefi: add query-firmware-log monitor command
2025-10-17 11:50 ` [PATCH v6 1/3] hw/uefi: add query-firmware-log monitor command Gerd Hoffmann
@ 2025-10-22 5:55 ` Markus Armbruster
0 siblings, 0 replies; 6+ messages in thread
From: Markus Armbruster @ 2025-10-22 5:55 UTC (permalink / raw)
To: Gerd Hoffmann
Cc: qemu-devel, Eric Blake, Marcel Apfelbaum, Eduardo Habkost,
Zhao Liu, Laurent Vivier, Philippe Mathieu-Daudé,
Paolo Bonzini, Fabiano Rosas, Dr. David Alan Gilbert, Yanan Wang
Gerd Hoffmann <kraxel@redhat.com> writes:
> Starting with the edk2-stable202508 tag OVMF (and ArmVirt too) have
> optional support for logging to a memory buffer. There is guest side
> support -- for example in linux kernels v6.17+ -- to read that buffer.
> But that might not helpful if your guest stops booting early enough that
> guest tooling can not be used yet. So host side support to read that
> log buffer is a useful thing to have.
>
> This patch implements the query-firmware-log qmp monitor command to
> read the firmware log.
>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v6 2/3] hw/uefi: add 'info firmware-log' hmp monitor command.
2025-10-17 11:50 [PATCH v6 0/3] hw/uefi: add support for receiving the firmware log via monitor Gerd Hoffmann
2025-10-17 11:50 ` [PATCH v6 1/3] hw/uefi: add query-firmware-log monitor command Gerd Hoffmann
@ 2025-10-17 11:50 ` Gerd Hoffmann
2025-10-17 11:50 ` [PATCH v6 3/3] hw/uefi/ovmf-log: add maxsize parameter Gerd Hoffmann
2 siblings, 0 replies; 6+ messages in thread
From: Gerd Hoffmann @ 2025-10-17 11:50 UTC (permalink / raw)
To: qemu-devel
Cc: Eric Blake, Marcel Apfelbaum, Eduardo Habkost, Zhao Liu,
Laurent Vivier, Philippe Mathieu-Daudé, Gerd Hoffmann,
Paolo Bonzini, Fabiano Rosas, Dr. David Alan Gilbert, Yanan Wang,
Markus Armbruster
This adds the hmp variant of the query-firmware-log qmp command.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
---
include/monitor/hmp.h | 1 +
hw/uefi/ovmf-log.c | 27 +++++++++++++++++++++++++++
hmp-commands-info.hx | 13 +++++++++++++
3 files changed, 41 insertions(+)
diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
index 897dfaa2b6d9..83721b5ffc6d 100644
--- a/include/monitor/hmp.h
+++ b/include/monitor/hmp.h
@@ -179,5 +179,6 @@ void hmp_boot_set(Monitor *mon, const QDict *qdict);
void hmp_info_mtree(Monitor *mon, const QDict *qdict);
void hmp_info_cryptodev(Monitor *mon, const QDict *qdict);
void hmp_dumpdtb(Monitor *mon, const QDict *qdict);
+void hmp_info_firmware_log(Monitor *mon, const QDict *qdict);
#endif
diff --git a/hw/uefi/ovmf-log.c b/hw/uefi/ovmf-log.c
index 0d4bd503a06a..fe8acbd19236 100644
--- a/hw/uefi/ovmf-log.c
+++ b/hw/uefi/ovmf-log.c
@@ -231,3 +231,30 @@ FirmwareLog *qmp_query_firmware_log(Error **errp)
ret->log = g_base64_encode((const guchar *)log->str, log->len);
return ret;
}
+
+void hmp_info_firmware_log(Monitor *mon, const QDict *qdict)
+{
+ g_autofree gchar *log_esc = NULL;
+ g_autofree guchar *log_out = NULL;
+ Error *err = NULL;
+ FirmwareLog *log;
+ gsize log_len;
+
+ log = qmp_query_firmware_log(&err);
+ if (err) {
+ hmp_handle_error(mon, err);
+ return;
+ }
+
+ g_assert(log != NULL);
+ g_assert(log->log != NULL);
+
+ if (log->version) {
+ g_autofree gchar *esc = g_strescape(log->version, NULL);
+ monitor_printf(mon, "[ firmware version: %s ]\n", esc);
+ }
+
+ log_out = g_base64_decode(log->log, &log_len);
+ log_esc = g_strescape((gchar *)log_out, "\r\n");
+ monitor_printf(mon, "%s\n", log_esc);
+}
diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
index 25b4aed51f56..33cf740bbc1b 100644
--- a/hmp-commands-info.hx
+++ b/hmp-commands-info.hx
@@ -995,3 +995,16 @@ SRST
``info cryptodev``
Show the crypto devices.
ERST
+
+ {
+ .name = "firmware-log",
+ .args_type = "",
+ .params = "",
+ .help = "show the firmware (ovmf) debug log",
+ .cmd = hmp_info_firmware_log,
+ },
+
+SRST
+ ``info firmware-log``
+ Show the firmware (ovmf) debug log.
+ERST
--
2.51.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH v6 3/3] hw/uefi/ovmf-log: add maxsize parameter
2025-10-17 11:50 [PATCH v6 0/3] hw/uefi: add support for receiving the firmware log via monitor Gerd Hoffmann
2025-10-17 11:50 ` [PATCH v6 1/3] hw/uefi: add query-firmware-log monitor command Gerd Hoffmann
2025-10-17 11:50 ` [PATCH v6 2/3] hw/uefi: add 'info firmware-log' hmp " Gerd Hoffmann
@ 2025-10-17 11:50 ` Gerd Hoffmann
2025-10-22 5:57 ` Markus Armbruster
2 siblings, 1 reply; 6+ messages in thread
From: Gerd Hoffmann @ 2025-10-17 11:50 UTC (permalink / raw)
To: qemu-devel
Cc: Eric Blake, Marcel Apfelbaum, Eduardo Habkost, Zhao Liu,
Laurent Vivier, Philippe Mathieu-Daudé, Gerd Hoffmann,
Paolo Bonzini, Fabiano Rosas, Dr. David Alan Gilbert, Yanan Wang,
Markus Armbruster
Allow limiting the amount of log output sent. Allow up to 1 MiB.
In case the guest log buffer is larger than 1 MiB limit the output
instead of throwing an error.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
hw/uefi/ovmf-log.c | 42 ++++++++++++++++++++++++++++++++++--------
hmp-commands-info.hx | 4 ++--
qapi/machine.json | 5 +++++
3 files changed, 41 insertions(+), 10 deletions(-)
diff --git a/hw/uefi/ovmf-log.c b/hw/uefi/ovmf-log.c
index fe8acbd19236..98ebb0209491 100644
--- a/hw/uefi/ovmf-log.c
+++ b/hw/uefi/ovmf-log.c
@@ -18,6 +18,7 @@
#include "qapi/error.h"
#include "qapi/type-helpers.h"
#include "qapi/qapi-commands-machine.h"
+#include "qobject/qdict.h"
/* ----------------------------------------------------------------------- */
@@ -164,7 +165,8 @@ static void handle_ovmf_log_range(GString *out,
}
}
-FirmwareLog *qmp_query_firmware_log(Error **errp)
+FirmwareLog *qmp_query_firmware_log(bool have_max_size, uint64_t max_size,
+ Error **errp)
{
MEM_DEBUG_LOG_HDR header;
dma_addr_t offset, base;
@@ -184,18 +186,40 @@ FirmwareLog *qmp_query_firmware_log(Error **errp)
return NULL;
}
- if (header.DebugLogSize > MiB) {
- /* default size is 128k (32 pages), allow up to 1M */
- error_setg(errp, "firmware log: log buffer is too big");
- return NULL;
- }
-
if (header.DebugLogHeadOffset > header.DebugLogSize ||
header.DebugLogTailOffset > header.DebugLogSize) {
error_setg(errp, "firmware log buffer header is invalid");
return NULL;
}
+ if (have_max_size) {
+ if (max_size > MiB) {
+ error_setg(errp, "parameter 'max-size' exceeds 1MiB");
+ return NULL;
+ }
+ } else {
+ max_size = MiB;
+ }
+
+ /* adjust header.DebugLogHeadOffset so we return at most maxsize bytes */
+ if (header.DebugLogHeadOffset > header.DebugLogTailOffset) {
+ /* wrap around */
+ if (header.DebugLogTailOffset > max_size) {
+ header.DebugLogHeadOffset = header.DebugLogTailOffset - max_size;
+ } else {
+ uint64_t max_chunk = max_size - header.DebugLogTailOffset;
+ if (header.DebugLogSize > max_chunk &&
+ header.DebugLogHeadOffset < header.DebugLogSize - max_chunk) {
+ header.DebugLogHeadOffset = header.DebugLogSize - max_chunk;
+ }
+ }
+ } else {
+ if (header.DebugLogTailOffset > max_size &&
+ header.DebugLogHeadOffset < header.DebugLogTailOffset - max_size) {
+ header.DebugLogHeadOffset = header.DebugLogTailOffset - max_size;
+ }
+ }
+
base = offset + header.HeaderSize;
if (header.DebugLogHeadOffset > header.DebugLogTailOffset) {
/* wrap around */
@@ -239,8 +263,10 @@ void hmp_info_firmware_log(Monitor *mon, const QDict *qdict)
Error *err = NULL;
FirmwareLog *log;
gsize log_len;
+ int64_t maxsize;
- log = qmp_query_firmware_log(&err);
+ maxsize = qdict_get_try_int(qdict, "max-size", -1);
+ log = qmp_query_firmware_log(maxsize != -1, (uint64_t)maxsize, &err);
if (err) {
hmp_handle_error(mon, err);
return;
diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
index 33cf740bbc1b..2a7f5810d706 100644
--- a/hmp-commands-info.hx
+++ b/hmp-commands-info.hx
@@ -998,8 +998,8 @@ ERST
{
.name = "firmware-log",
- .args_type = "",
- .params = "",
+ .args_type = "max-size:o?",
+ .params = "[max-size]",
.help = "show the firmware (ovmf) debug log",
.cmd = hmp_info_firmware_log,
},
diff --git a/qapi/machine.json b/qapi/machine.json
index 96133e5c71cf..c6dc6fe69b5c 100644
--- a/qapi/machine.json
+++ b/qapi/machine.json
@@ -1858,9 +1858,14 @@
#
# Find firmware memory log buffer in guest memory, return content.
#
+# @max-size: limit the amount of log data returned. Up to 1 MiB of
+# log data is allowed. In case the amount of log data is
+# larger than @max-size the tail of the log is returned.
+#
# Since: 10.2
##
{ 'command': 'query-firmware-log',
+ 'data': { '*max-size': 'size' },
'returns': 'FirmwareLog' }
##
--
2.51.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH v6 3/3] hw/uefi/ovmf-log: add maxsize parameter
2025-10-17 11:50 ` [PATCH v6 3/3] hw/uefi/ovmf-log: add maxsize parameter Gerd Hoffmann
@ 2025-10-22 5:57 ` Markus Armbruster
0 siblings, 0 replies; 6+ messages in thread
From: Markus Armbruster @ 2025-10-22 5:57 UTC (permalink / raw)
To: Gerd Hoffmann
Cc: qemu-devel, Eric Blake, Marcel Apfelbaum, Eduardo Habkost,
Zhao Liu, Laurent Vivier, Philippe Mathieu-Daudé,
Paolo Bonzini, Fabiano Rosas, Dr. David Alan Gilbert, Yanan Wang
Gerd Hoffmann <kraxel@redhat.com> writes:
> Allow limiting the amount of log output sent. Allow up to 1 MiB.
> In case the guest log buffer is larger than 1 MiB limit the output
> instead of throwing an error.
>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
^ permalink raw reply [flat|nested] 6+ messages in thread