[PATCH v4 0/2] hw/uefi: add support for receiving the firmware log via monitor.

[PATCH v4 0/2] hw/uefi: add support for receiving the firmware log via monitor.

[Gerd Hoffmann]

Gerd Hoffmann (2):
  hw/uefi: add "info firmware-log" + "query-firmware-log" monitor
    commands
  hw/uefi/ovmf-log: add maxsize parameter

 include/monitor/hmp.h      |   1 +
 hw/uefi/ovmf-log.c         | 291 +++++++++++++++++++++++++++++++++++++
 tests/qtest/qmp-cmd-test.c |   2 +
 hmp-commands-info.hx       |  13 ++
 hw/uefi/meson.build        |   2 +-
 qapi/machine.json          |  26 ++++
 6 files changed, 334 insertions(+), 1 deletion(-)
 create mode 100644 hw/uefi/ovmf-log.c

-- 
2.51.0

[PATCH v4 1/2] hw/uefi: add "info firmware-log" + "query-firmware-log" monitor commands

[Gerd Hoffmann]

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 both qmp and hmp monitor commands to read the
firmware log.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 include/monitor/hmp.h      |   1 +
 hw/uefi/ovmf-log.c         | 267 +++++++++++++++++++++++++++++++++++++
 tests/qtest/qmp-cmd-test.c |   2 +
 hmp-commands-info.hx       |  14 ++
 hw/uefi/meson.build        |   2 +-
 qapi/machine.json          |  23 ++++
 6 files changed, 308 insertions(+), 1 deletion(-)
 create mode 100644 hw/uefi/ovmf-log.c

diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
index ae116d9804a3..885c0ecd2aed 100644
--- a/include/monitor/hmp.h
+++ b/include/monitor/hmp.h
@@ -178,5 +178,6 @@ 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
new file mode 100644
index 000000000000..f03e47a290d6
--- /dev/null
+++ b/hw/uefi/ovmf-log.c
@@ -0,0 +1,267 @@
+/*
+ * 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/base64.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;
+} MEM_DEBUG_LOG_MAGIC;
+
+/* 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 MEM_DEBUG_LOG_MAGIC magic = {
+        .magic1 = MEM_DEBUG_LOG_MAGIC1,
+        .magic2 = MEM_DEBUG_LOG_MAGIC2,
+    };
+    MEM_DEBUG_LOG_MAGIC 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)
+{
+    g_autofree char *buf = NULL;
+
+    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, "firmware log: buffer read error");
+        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: not found");
+        return NULL;
+    }
+
+    if (dma_memory_read(&address_space_memory, offset,
+                        &header, sizeof(header),
+                        MEMTXATTRS_UNSPECIFIED)) {
+        error_setg(errp, "firmware log: header read error");
+        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: invalid header");
+        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);
+    ret->version = g_strndup(header.FirmwareVersion,
+                             sizeof(header.FirmwareVersion));
+    ret->log = g_base64_encode((const guchar *)log->str, log->len);
+    return ret;
+}
+
+void hmp_info_firmware_log(Monitor *mon, const QDict *qdict)
+{
+    Error *errp = NULL;
+    FirmwareLog *log;
+
+    log = qmp_query_firmware_log(&errp);
+    if (errp)  {
+        hmp_handle_error(mon, errp);
+        return;
+    }
+
+    g_assert(log != NULL);
+
+    if (log->version) {
+        g_autofree gchar *esc = g_strescape(log->version, NULL);
+        monitor_printf(mon, "[ firmware version: %s ]\n", esc);
+    }
+
+    if (log->log) {
+        g_autofree gchar *esc = NULL;
+        g_autofree gchar *out = NULL;
+        size_t outlen;
+
+        out = (gchar *)qbase64_decode(log->log, -1, &outlen, &errp);
+        if (errp)  {
+            hmp_handle_error(mon, errp);
+            return;
+        }
+        esc = g_strescape(out, "\r\n");
+        monitor_printf(mon, "%s\n", esc);
+    }
+}
diff --git a/tests/qtest/qmp-cmd-test.c b/tests/qtest/qmp-cmd-test.c
index cf718761861d..ffdb7e979e0f 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-ovmf-log", ERROR_CLASS_GENERIC_ERROR },
         { NULL, -1 }
     };
     int i;
diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
index 6142f60e7b16..257015f0b403 100644
--- a/hmp-commands-info.hx
+++ b/hmp-commands-info.hx
@@ -977,3 +977,17 @@ 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,
+        .flags      = "p",
+    },
+
+SRST
+  ``info firmware-log``
+    Show the firmware (ovmf) debug log.
+ERST
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..c96e582afdd6 100644
--- a/qapi/machine.json
+++ b/qapi/machine.json
@@ -1839,6 +1839,29 @@
   'returns': 'HumanReadableText',
   'features': [ 'unstable' ]}
 
+##
+# @FirmwareLog:
+#
+# @version: Firmware version.
+#
+# @log: Firmware debug log, in base64 encoding.
+#
+# 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

Re: [PATCH v4 1/2] hw/uefi: add "info firmware-log" + "query-firmware-log" monitor commands

[Daniel P. Berrangé]

On Mon, Oct 13, 2025 at 12:49:53PM +0200, Gerd Hoffmann wrote:
> 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 both qmp and hmp monitor commands to read the
> firmware log.
> 
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  include/monitor/hmp.h      |   1 +
>  hw/uefi/ovmf-log.c         | 267 +++++++++++++++++++++++++++++++++++++
>  tests/qtest/qmp-cmd-test.c |   2 +
>  hmp-commands-info.hx       |  14 ++
>  hw/uefi/meson.build        |   2 +-
>  qapi/machine.json          |  23 ++++
>  6 files changed, 308 insertions(+), 1 deletion(-)
>  create mode 100644 hw/uefi/ovmf-log.c
> 
> diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
> index ae116d9804a3..885c0ecd2aed 100644
> --- a/include/monitor/hmp.h
> +++ b/include/monitor/hmp.h
> @@ -178,5 +178,6 @@ 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
> new file mode 100644
> index 000000000000..f03e47a290d6
> --- /dev/null
> +++ b/hw/uefi/ovmf-log.c
> @@ -0,0 +1,267 @@
> +/*
> + * 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/base64.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;
> +} MEM_DEBUG_LOG_MAGIC;
> +
> +/* 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 MEM_DEBUG_LOG_MAGIC magic = {
> +        .magic1 = MEM_DEBUG_LOG_MAGIC1,
> +        .magic2 = MEM_DEBUG_LOG_MAGIC2,
> +    };
> +    MEM_DEBUG_LOG_MAGIC 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)
> +{
> +    g_autofree char *buf = NULL;

Left-over variable - unfortunately gcc doens't warn about unused
vars when g_autofree is present :-(

> +
> +    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, "firmware log: buffer read error");
> +        return;
> +    }
> +}

> diff --git a/qapi/machine.json b/qapi/machine.json
> index 038eab281c78..c96e582afdd6 100644
> --- a/qapi/machine.json
> +++ b/qapi/machine.json
> @@ -1839,6 +1839,29 @@
>    'returns': 'HumanReadableText',
>    'features': [ 'unstable' ]}
>  
> +##
> +# @FirmwareLog:
> +#
> +# @version: Firmware version.
> +#
> +# @log: Firmware debug log, in base64 encoding.
> +#
> +# Since: 10.2
> +##
> +{ 'struct': 'FirmwareLog',
> +  'data': { '*version': 'str',
> +            '*log': 'str' } }

Having version be optional makes sense, but what is the semantics for
'log' being optional. If the log is unavailable, wouldn't we be better
raising an error ?


With regards,
Daniel
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Re: [PATCH v4 1/2] hw/uefi: add "info firmware-log" + "query-firmware-log" monitor commands

[Gerd Hoffmann]

  Hi,

> > +static void handle_ovmf_log_range(GString *out,
> > +                                  dma_addr_t start,
> > +                                  dma_addr_t end,
> > +                                  Error **errp)
> > +{
> > +    g_autofree char *buf = NULL;
> 
> Left-over variable - unfortunately gcc doens't warn about unused
> vars when g_autofree is present :-(

Fixed.

> > +{ 'struct': 'FirmwareLog',
> > +  'data': { '*version': 'str',
> > +            '*log': 'str' } }
> 
> Having version be optional makes sense, but what is the semantics for
> 'log' being optional. If the log is unavailable, wouldn't we be better
> raising an error ?

That is what the current implementation actually does.  I change it.

take care,
  Gerd

Re: [PATCH v4 1/2] hw/uefi: add "info firmware-log" + "query-firmware-log" monitor commands

[Markus Armbruster]

Gerd Hoffmann <kraxel@redhat.com> writes:

>   Hi,
>
>> > +static void handle_ovmf_log_range(GString *out,
>> > +                                  dma_addr_t start,
>> > +                                  dma_addr_t end,
>> > +                                  Error **errp)
>> > +{
>> > +    g_autofree char *buf = NULL;
>> 
>> Left-over variable - unfortunately gcc doens't warn about unused
>> vars when g_autofree is present :-(
>
> Fixed.
>
>> > +{ 'struct': 'FirmwareLog',
>> > +  'data': { '*version': 'str',
>> > +            '*log': 'str' } }
>> 
>> Having version be optional makes sense, but what is the semantics for
>> 'log' being optional. If the log is unavailable, wouldn't we be better
>> raising an error ?
>
> That is what the current implementation actually does.  I change it.

Drawback: when some Firmware provides version, but not log, the command
can't give us the version, because it fails.  Do we care?

Re: [PATCH v4 1/2] hw/uefi: add "info firmware-log" + "query-firmware-log" monitor commands

[Gerd Hoffmann]

On Wed, Oct 15, 2025 at 09:41:15AM +0200, Markus Armbruster wrote:
> Gerd Hoffmann <kraxel@redhat.com> writes:
> 
> >   Hi,
> >
> >> > +static void handle_ovmf_log_range(GString *out,
> >> > +                                  dma_addr_t start,
> >> > +                                  dma_addr_t end,
> >> > +                                  Error **errp)
> >> > +{
> >> > +    g_autofree char *buf = NULL;
> >> 
> >> Left-over variable - unfortunately gcc doens't warn about unused
> >> vars when g_autofree is present :-(
> >
> > Fixed.
> >
> >> > +{ 'struct': 'FirmwareLog',
> >> > +  'data': { '*version': 'str',
> >> > +            '*log': 'str' } }
> >> 
> >> Having version be optional makes sense, but what is the semantics for
> >> 'log' being optional. If the log is unavailable, wouldn't we be better
> >> raising an error ?
> >
> > That is what the current implementation actually does.  I change it.
> 
> Drawback: when some Firmware provides version, but not log, the command
> can't give us the version, because it fails.  Do we care?

Technically the current implementation has both version and log,
unconditionally, even though both can be the empty string ...

take care,
  Gerd

Re: [PATCH v4 1/2] hw/uefi: add "info firmware-log" + "query-firmware-log" monitor commands

[Daniel P. Berrangé]

On Wed, Oct 15, 2025 at 09:41:15AM +0200, Markus Armbruster wrote:
> Gerd Hoffmann <kraxel@redhat.com> writes:
> 
> >   Hi,
> >
> >> > +static void handle_ovmf_log_range(GString *out,
> >> > +                                  dma_addr_t start,
> >> > +                                  dma_addr_t end,
> >> > +                                  Error **errp)
> >> > +{
> >> > +    g_autofree char *buf = NULL;
> >> 
> >> Left-over variable - unfortunately gcc doens't warn about unused
> >> vars when g_autofree is present :-(
> >
> > Fixed.
> >
> >> > +{ 'struct': 'FirmwareLog',
> >> > +  'data': { '*version': 'str',
> >> > +            '*log': 'str' } }
> >> 
> >> Having version be optional makes sense, but what is the semantics for
> >> 'log' being optional. If the log is unavailable, wouldn't we be better
> >> raising an error ?
> >
> > That is what the current implementation actually does.  I change it.
> 
> Drawback: when some Firmware provides version, but not log, the command
> can't give us the version, because it fails.  Do we care?

This command is literally called 'query-firmware-log' though. From this
I consider the log to be the important deliverable. If not available then
I would expect an error from such a named command. If we want to provide
non-log related info about the firmware when no log is available, then we
should rename the command to "query-firmware-info" instead.

With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|

Re: [PATCH v4 1/2] hw/uefi: add "info firmware-log" + "query-firmware-log" monitor commands

[Markus Armbruster]

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 both qmp and hmp monitor commands to read the
> firmware log.
>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  include/monitor/hmp.h      |   1 +
>  hw/uefi/ovmf-log.c         | 267 +++++++++++++++++++++++++++++++++++++
>  tests/qtest/qmp-cmd-test.c |   2 +
>  hmp-commands-info.hx       |  14 ++
>  hw/uefi/meson.build        |   2 +-
>  qapi/machine.json          |  23 ++++
>  6 files changed, 308 insertions(+), 1 deletion(-)
>  create mode 100644 hw/uefi/ovmf-log.c
>
> diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
> index ae116d9804a3..885c0ecd2aed 100644
> --- a/include/monitor/hmp.h
> +++ b/include/monitor/hmp.h
> @@ -178,5 +178,6 @@ 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
> new file mode 100644
> index 000000000000..f03e47a290d6
> --- /dev/null
> +++ b/hw/uefi/ovmf-log.c
> @@ -0,0 +1,267 @@
> +/*
> + * 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/base64.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;
> +} MEM_DEBUG_LOG_MAGIC;

You changed capitalization.  Intentional?

> +
> +/* 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 MEM_DEBUG_LOG_MAGIC magic = {
> +        .magic1 = MEM_DEBUG_LOG_MAGIC1,
> +        .magic2 = MEM_DEBUG_LOG_MAGIC2,
> +    };
> +    MEM_DEBUG_LOG_MAGIC 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)
> +{
> +    g_autofree char *buf = NULL;
> +
> +    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, "firmware log: buffer read error");
> +        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: not found");
> +        return NULL;
> +    }
> +
> +    if (dma_memory_read(&address_space_memory, offset,
> +                        &header, sizeof(header),
> +                        MEMTXATTRS_UNSPECIFIED)) {
> +        error_setg(errp, "firmware log: header read error");
> +        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: invalid header");
> +        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);
> +    ret->version = g_strndup(header.FirmwareVersion,
> +                             sizeof(header.FirmwareVersion));
> +    ret->log = g_base64_encode((const guchar *)log->str, log->len);
> +    return ret;
> +}
> +
> +void hmp_info_firmware_log(Monitor *mon, const QDict *qdict)
> +{
> +    Error *errp = NULL;

Unusual identifier.  By convention, we use @errp for Error **, and @err
for Error *.  Missed this in v3, sorry.

> +    FirmwareLog *log;
> +
> +    log = qmp_query_firmware_log(&errp);
> +    if (errp)  {
> +        hmp_handle_error(mon, errp);
> +        return;
> +    }
> +
> +    g_assert(log != NULL);
> +
> +    if (log->version) {
> +        g_autofree gchar *esc = g_strescape(log->version, NULL);
> +        monitor_printf(mon, "[ firmware version: %s ]\n", esc);
> +    }
> +
> +    if (log->log) {
> +        g_autofree gchar *esc = NULL;
> +        g_autofree gchar *out = NULL;
> +        size_t outlen;
> +
> +        out = (gchar *)qbase64_decode(log->log, -1, &outlen, &errp);
> +        if (errp)  {

How can this happen?

> +            hmp_handle_error(mon, errp);
> +            return;
> +        }
> +        esc = g_strescape(out, "\r\n");
> +        monitor_printf(mon, "%s\n", esc);
> +    }
> +}
> diff --git a/tests/qtest/qmp-cmd-test.c b/tests/qtest/qmp-cmd-test.c
> index cf718761861d..ffdb7e979e0f 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-ovmf-log", ERROR_CLASS_GENERIC_ERROR },
>          { NULL, -1 }
>      };
>      int i;
> diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
> index 6142f60e7b16..257015f0b403 100644
> --- a/hmp-commands-info.hx
> +++ b/hmp-commands-info.hx
> @@ -977,3 +977,17 @@ 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,
> +        .flags      = "p",
> +    },
> +
> +SRST
> +  ``info firmware-log``
> +    Show the firmware (ovmf) debug log.
> +ERST
> 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..c96e582afdd6 100644
> --- a/qapi/machine.json
> +++ b/qapi/machine.json
> @@ -1839,6 +1839,29 @@
>    'returns': 'HumanReadableText',
>    'features': [ 'unstable' ]}
>  
> +##
> +# @FirmwareLog:
> +#
> +# @version: Firmware version.
> +#
> +# @log: Firmware debug log, in base64 encoding.

Recomment to document that @log can start and end with a partial line.

> +#
> +# 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:
>  #

Re: [PATCH v4 1/2] hw/uefi: add "info firmware-log" + "query-firmware-log" monitor commands

[Gerd Hoffmann]

> > +/* ----------------------------------------------------------------------- */
> > +/* qemu monitor command                                                    */
> > +
> > +typedef struct {
> > +    uint64_t             magic1;
> > +    uint64_t             magic2;
> > +} MEM_DEBUG_LOG_MAGIC;
> 
> You changed capitalization.  Intentional?

Reduce the qemu / edk2 code style mix a bit ...

> > +    if (log->log) {
> > +        g_autofree gchar *esc = NULL;
> > +        g_autofree gchar *out = NULL;
> > +        size_t outlen;
> > +
> > +        out = (gchar *)qbase64_decode(log->log, -1, &outlen, &errp);
> > +        if (errp)  {
> 
> How can this happen?

In theory it should never happen.

take care,
  Gerd

Re: [PATCH v4 1/2] hw/uefi: add "info firmware-log" + "query-firmware-log" monitor commands

[Markus Armbruster]

Gerd Hoffmann <kraxel@redhat.com> writes:

>> > +/* ----------------------------------------------------------------------- */
>> > +/* qemu monitor command                                                    */
>> > +
>> > +typedef struct {
>> > +    uint64_t             magic1;
>> > +    uint64_t             magic2;
>> > +} MEM_DEBUG_LOG_MAGIC;
>> 
>> You changed capitalization.  Intentional?
>
> Reduce the qemu / edk2 code style mix a bit ...

Up to you, but I'd use Magic with MEM_DEBUG_LOG_MAGIC, and magic with
something like MemDebugLogMagic.

>> > +    if (log->log) {
>> > +        g_autofree gchar *esc = NULL;
>> > +        g_autofree gchar *out = NULL;
>> > +        size_t outlen;
>> > +
>> > +        out = (gchar *)qbase64_decode(log->log, -1, &outlen, &errp);
>> > +        if (errp)  {
>> 
>> How can this happen?
>
> In theory it should never happen.

Pass &error_abort then.  Avoids untestable error path.

Actually, just use g_base64_decode().

[PATCH v4 2/2] hw/uefi/ovmf-log: add maxsize parameter

[Gerd Hoffmann]

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   | 40 ++++++++++++++++++++++++++++++++--------
 hmp-commands-info.hx |  5 ++---
 qapi/machine.json    |  3 +++
 3 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/hw/uefi/ovmf-log.c b/hw/uefi/ovmf-log.c
index f03e47a290d6..9d9dc7b0d8d5 100644
--- a/hw/uefi/ovmf-log.c
+++ b/hw/uefi/ovmf-log.c
@@ -19,6 +19,7 @@
 #include "qapi/error.h"
 #include "qapi/type-helpers.h"
 #include "qapi/qapi-commands-machine.h"
+#include "qobject/qdict.h"
 
 
 /* ----------------------------------------------------------------------- */
@@ -167,7 +168,8 @@ static void handle_ovmf_log_range(GString *out,
     }
 }
 
-FirmwareLog *qmp_query_firmware_log(Error **errp)
+FirmwareLog *qmp_query_firmware_log(bool have_maxsize, uint64_t maxsize,
+                                    Error **errp)
 {
     MEM_DEBUG_LOG_HDR header;
     dma_addr_t offset, base;
@@ -187,18 +189,38 @@ 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: invalid header");
         return NULL;
     }
 
+    if (!have_maxsize) {
+        maxsize = MiB;
+    }
+    if (maxsize > MiB) {
+        maxsize = MiB;
+    }
+
+    /* adjust header.DebugLogHeadOffset so we rezturn at most maxsize bytes */
+    if (header.DebugLogHeadOffset > header.DebugLogTailOffset) {
+        /* wrap around */
+        if (header.DebugLogTailOffset > maxsize) {
+            header.DebugLogHeadOffset = header.DebugLogTailOffset - maxsize;
+        } else {
+            uint64_t maxchunk = maxsize - header.DebugLogTailOffset;
+            if (header.DebugLogSize > maxchunk &&
+                header.DebugLogHeadOffset < header.DebugLogSize - maxchunk) {
+                header.DebugLogHeadOffset = header.DebugLogSize - maxchunk;
+            }
+        }
+    } else {
+        if (header.DebugLogTailOffset > maxsize &&
+            header.DebugLogHeadOffset < header.DebugLogTailOffset - maxsize) {
+            header.DebugLogHeadOffset = header.DebugLogTailOffset - maxsize;
+        }
+    }
+
     base = offset + header.HeaderSize;
     if (header.DebugLogHeadOffset > header.DebugLogTailOffset) {
         /* wrap around */
@@ -237,8 +259,10 @@ void hmp_info_firmware_log(Monitor *mon, const QDict *qdict)
 {
     Error *errp = NULL;
     FirmwareLog *log;
+    int64_t maxsize;
 
-    log = qmp_query_firmware_log(&errp);
+    maxsize = qdict_get_try_int(qdict, "maxsize", -1);
+    log = qmp_query_firmware_log(maxsize != -1, (uint64_t)maxsize, &errp);
     if (errp)  {
         hmp_handle_error(mon, errp);
         return;
diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
index 257015f0b403..db03d88d3c74 100644
--- a/hmp-commands-info.hx
+++ b/hmp-commands-info.hx
@@ -980,11 +980,10 @@ ERST
 
     {
         .name       = "firmware-log",
-        .args_type  = "",
-        .params     = "",
+        .args_type  = "maxsize:i?",
+        .params     = "[maxsize]",
         .help       = "show the firmware (ovmf) debug log",
         .cmd        = hmp_info_firmware_log,
-        .flags      = "p",
     },
 
 SRST
diff --git a/qapi/machine.json b/qapi/machine.json
index c96e582afdd6..d0c6d3ede027 100644
--- a/qapi/machine.json
+++ b/qapi/machine.json
@@ -1857,9 +1857,12 @@
 #
 # Find firmware memory log buffer in guest memory, return content.
 #
+# @maxsize: limit the amount of logdata returned.
+#
 # Since: 10.2
 ##
 { 'command': 'query-firmware-log',
+  'data': { '*maxsize': 'size' },
   'returns': 'FirmwareLog' }
 
 ##
-- 
2.51.0

Re: [PATCH v4 2/2] hw/uefi/ovmf-log: add maxsize parameter

[Daniel P. Berrangé]

On Mon, Oct 13, 2025 at 12:49:54PM +0200, Gerd Hoffmann wrote:
> 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   | 40 ++++++++++++++++++++++++++++++++--------
>  hmp-commands-info.hx |  5 ++---
>  qapi/machine.json    |  3 +++
>  3 files changed, 37 insertions(+), 11 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


With regards,
Daniel
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Re: [PATCH v4 2/2] hw/uefi/ovmf-log: add maxsize parameter

[Markus Armbruster]

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>
> ---
>  hw/uefi/ovmf-log.c   | 40 ++++++++++++++++++++++++++++++++--------
>  hmp-commands-info.hx |  5 ++---
>  qapi/machine.json    |  3 +++
>  3 files changed, 37 insertions(+), 11 deletions(-)
>
> diff --git a/hw/uefi/ovmf-log.c b/hw/uefi/ovmf-log.c
> index f03e47a290d6..9d9dc7b0d8d5 100644
> --- a/hw/uefi/ovmf-log.c
> +++ b/hw/uefi/ovmf-log.c
> @@ -19,6 +19,7 @@
>  #include "qapi/error.h"
>  #include "qapi/type-helpers.h"
>  #include "qapi/qapi-commands-machine.h"
> +#include "qobject/qdict.h"
>  
>  
>  /* ----------------------------------------------------------------------- */
> @@ -167,7 +168,8 @@ static void handle_ovmf_log_range(GString *out,
>      }
>  }
>  
> -FirmwareLog *qmp_query_firmware_log(Error **errp)
> +FirmwareLog *qmp_query_firmware_log(bool have_maxsize, uint64_t maxsize,
> +                                    Error **errp)
>  {
>      MEM_DEBUG_LOG_HDR header;
>      dma_addr_t offset, base;
> @@ -187,18 +189,38 @@ 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: invalid header");
>          return NULL;
>      }
>  
> +    if (!have_maxsize) {
> +        maxsize = MiB;
> +    }
> +    if (maxsize > MiB) {
> +        maxsize = MiB;

Silently "fixing" the user's instructions is rarely a good idea.  Either
don't limit the argument (if the user asks for rope...), or make
exceeding the limit an error.

> +    }
> +
> +    /* adjust header.DebugLogHeadOffset so we rezturn at most maxsize bytes */
> +    if (header.DebugLogHeadOffset > header.DebugLogTailOffset) {
> +        /* wrap around */
> +        if (header.DebugLogTailOffset > maxsize) {
> +            header.DebugLogHeadOffset = header.DebugLogTailOffset - maxsize;
> +        } else {
> +            uint64_t maxchunk = maxsize - header.DebugLogTailOffset;
> +            if (header.DebugLogSize > maxchunk &&
> +                header.DebugLogHeadOffset < header.DebugLogSize - maxchunk) {
> +                header.DebugLogHeadOffset = header.DebugLogSize - maxchunk;
> +            }
> +        }
> +    } else {
> +        if (header.DebugLogTailOffset > maxsize &&
> +            header.DebugLogHeadOffset < header.DebugLogTailOffset - maxsize) {
> +            header.DebugLogHeadOffset = header.DebugLogTailOffset - maxsize;
> +        }
> +    }
> +
>      base = offset + header.HeaderSize;
>      if (header.DebugLogHeadOffset > header.DebugLogTailOffset) {
>          /* wrap around */
> @@ -237,8 +259,10 @@ void hmp_info_firmware_log(Monitor *mon, const QDict *qdict)
>  {
>      Error *errp = NULL;
>      FirmwareLog *log;
> +    int64_t maxsize;
>  
> -    log = qmp_query_firmware_log(&errp);
> +    maxsize = qdict_get_try_int(qdict, "maxsize", -1);
> +    log = qmp_query_firmware_log(maxsize != -1, (uint64_t)maxsize, &errp);

Put a pin here.

>      if (errp)  {
>          hmp_handle_error(mon, errp);
>          return;
> diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
> index 257015f0b403..db03d88d3c74 100644
> --- a/hmp-commands-info.hx
> +++ b/hmp-commands-info.hx
> @@ -980,11 +980,10 @@ ERST
>  
>      {
>          .name       = "firmware-log",
> -        .args_type  = "",
> -        .params     = "",
> +        .args_type  = "maxsize:i?",

args_type 'i' is a 32 bit signed integer, so this gives us 31 bits.
Suffices.  But what happens when the user specifies a negative number?
I think hmp_info_firmware_log() treats -1 as if the parameter was
omitted.  qmp_query_firmware_log() then defaults to 1MiB.  Any other
negative number hmp_info_firmware_log() turns into a huge positive
number, which qmp_query_firmware_log() silently limits to 1MiB (but I
recommended not to do that).

Let's use 'o' instead of 'i'.  Enables convenient syntax like "64k".  63
bits.  No risk of sign accidents.

> +        .params     = "[maxsize]",
>          .help       = "show the firmware (ovmf) debug log",
>          .cmd        = hmp_info_firmware_log,
> -        .flags      = "p",

Accident?

>      },
>  
>  SRST
> diff --git a/qapi/machine.json b/qapi/machine.json
> index c96e582afdd6..d0c6d3ede027 100644
> --- a/qapi/machine.json
> +++ b/qapi/machine.json
> @@ -1857,9 +1857,12 @@
>  #
>  # Find firmware memory log buffer in guest memory, return content.
>  #
> +# @maxsize: limit the amount of logdata returned.

Please spell it @max-size.  We already use that spelling in this file.

"logdata" isn't a word.

The 1MiB limit for @maxsize needs to be documented (if we keep it).

Recommend to spell out that the command returns the tail of the log
buffer when it can't return all of it.

> +#
>  # Since: 10.2
>  ##
>  { 'command': 'query-firmware-log',
> +  'data': { '*maxsize': 'size' },
>    'returns': 'FirmwareLog' }
>  
>  ##