If the "etc/vmcoreinfo" fw_cfg file is present and we are not running
the kdump kernel, write the addr/size of the vmcoreinfo ELF note.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Gabriel Somlo <somlo@cmu.edu>
---
 drivers/firmware/qemu_fw_cfg.c | 87 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 86 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
index 2ac4cd869fe6..7a70e7a549f6 100644
--- a/drivers/firmware/qemu_fw_cfg.c
+++ b/drivers/firmware/qemu_fw_cfg.c
@@ -35,6 +35,8 @@
 #include <linux/ioport.h>
 #include <linux/delay.h>
 #include <linux/dma-mapping.h>
+#include <linux/crash_core.h>
+#include <linux/crash_dump.h>
 
 MODULE_AUTHOR("Gabriel L. Somlo <somlo@cmu.edu>");
 MODULE_DESCRIPTION("QEMU fw_cfg sysfs support");
@@ -59,6 +61,8 @@ MODULE_LICENSE("GPL");
 /* fw_cfg "file name" is up to 56 characters (including terminating nul) */
 #define FW_CFG_MAX_FILE_PATH 56
 
+#define VMCOREINFO_FORMAT_ELF 0x1
+
 /* platform device for dma mapping */
 static struct device *dev;
 
@@ -127,7 +131,8 @@ static ssize_t fw_cfg_dma_transfer(void *address, u32 length, u32 control)
 	dma_addr_t dma;
 	ssize_t ret = length;
 	enum dma_data_direction dir =
-		(control & FW_CFG_DMA_CTL_READ ? DMA_FROM_DEVICE : 0);
+		(control & FW_CFG_DMA_CTL_READ ? DMA_FROM_DEVICE : 0) |
+		(control & FW_CFG_DMA_CTL_WRITE ? DMA_TO_DEVICE : 0);
 
 	if (address && length) {
 		dma_addr = dma_map_single(dev, address, length, dir);
@@ -225,6 +230,48 @@ static ssize_t fw_cfg_read_blob(u16 key,
 	return ret;
 }
 
+#ifdef CONFIG_CRASH_CORE
+/* write chunk of given fw_cfg blob (caller responsible for sanity-check) */
+static ssize_t fw_cfg_write_blob(u16 key,
+				 void *buf, loff_t pos, size_t count)
+{
+	u32 glk = -1U;
+	acpi_status status;
+	ssize_t ret = count;
+
+	/* If we have ACPI, ensure mutual exclusion against any potential
+	 * device access by the firmware, e.g. via AML methods:
+	 */
+	status = acpi_acquire_global_lock(ACPI_WAIT_FOREVER, &glk);
+	if (ACPI_FAILURE(status) && status != AE_NOT_CONFIGURED) {
+		/* Should never get here */
+		WARN(1, "%s: Failed to lock ACPI!\n", __func__);
+		memset(buf, 0, count);
+		return -EINVAL;
+	}
+
+	mutex_lock(&fw_cfg_dev_lock);
+	if (pos == 0) {
+		ret = fw_cfg_dma_transfer(buf, count, key << 16
+					  | FW_CFG_DMA_CTL_SELECT
+					  | FW_CFG_DMA_CTL_WRITE);
+	} else {
+		iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
+		ret = fw_cfg_dma_transfer(NULL, pos, FW_CFG_DMA_CTL_SKIP);
+		if (ret < 0)
+			goto end;
+		ret = fw_cfg_dma_transfer(buf, count, FW_CFG_DMA_CTL_WRITE);
+	}
+
+end:
+	mutex_unlock(&fw_cfg_dev_lock);
+
+	acpi_release_global_lock(glk);
+
+	return ret;
+}
+#endif /* CONFIG_CRASH_CORE */
+
 /* clean up fw_cfg device i/o */
 static void fw_cfg_io_cleanup(void)
 {
@@ -343,6 +390,37 @@ struct fw_cfg_sysfs_entry {
 	struct list_head list;
 };
 
+#ifdef CONFIG_CRASH_CORE
+static ssize_t write_vmcoreinfo(const struct fw_cfg_file *f)
+{
+	struct vmci {
+		__le16 host_format;
+		__le16 guest_format;
+		__le32 size;
+		__le64 paddr;
+	} __packed;
+	struct vmci *data;
+	ssize_t ret;
+
+	data = kmalloc(sizeof(struct vmci), GFP_KERNEL | GFP_DMA);
+	if (!data)
+		return -ENOMEM;
+
+	/* spare ourself reading host format support for now since we
+	 * don't know what else to format - host may ignore ours
+	 */
+	*data = (struct vmci) {
+		.guest_format = cpu_to_le16(VMCOREINFO_FORMAT_ELF),
+		.size = cpu_to_le32(VMCOREINFO_NOTE_SIZE),
+		.paddr = cpu_to_le64(paddr_vmcoreinfo_note())
+	};
+	ret = fw_cfg_write_blob(f->select, data, 0, sizeof(struct vmci));
+
+	kfree(data);
+	return ret;
+}
+#endif /* CONFIG_CRASH_CORE */
+
 /* get fw_cfg_sysfs_entry from kobject member */
 static inline struct fw_cfg_sysfs_entry *to_entry(struct kobject *kobj)
 {
@@ -582,6 +660,13 @@ static int fw_cfg_register_file(const struct fw_cfg_file *f)
 	int err;
 	struct fw_cfg_sysfs_entry *entry;
 
+#ifdef CONFIG_CRASH_CORE
+	if (strcmp(f->name, "etc/vmcoreinfo") == 0 && !is_kdump_kernel()) {
+		if (write_vmcoreinfo(f) < 0)
+			pr_warn("fw_cfg: failed to write vmcoreinfo");
+	}
+#endif
+
 	/* allocate new entry */
 	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
 	if (!entry)
-- 
2.15.0.125.g8f49766d64

On Mon, Nov 13, 2017 at 08:29:58PM +0100, Marc-André Lureau wrote:
> If the "etc/vmcoreinfo" fw_cfg file is present and we are not running
> the kdump kernel, write the addr/size of the vmcoreinfo ELF note.
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> Reviewed-by: Gabriel Somlo <somlo@cmu.edu>
> ---
>  drivers/firmware/qemu_fw_cfg.c | 87 +++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 86 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
> index 2ac4cd869fe6..7a70e7a549f6 100644
> --- a/drivers/firmware/qemu_fw_cfg.c
> +++ b/drivers/firmware/qemu_fw_cfg.c
> @@ -35,6 +35,8 @@
>  #include <linux/ioport.h>
>  #include <linux/delay.h>
>  #include <linux/dma-mapping.h>
> +#include <linux/crash_core.h>
> +#include <linux/crash_dump.h>
>  
>  MODULE_AUTHOR("Gabriel L. Somlo <somlo@cmu.edu>");
>  MODULE_DESCRIPTION("QEMU fw_cfg sysfs support");
> @@ -59,6 +61,8 @@ MODULE_LICENSE("GPL");
>  /* fw_cfg "file name" is up to 56 characters (including terminating nul) */
>  #define FW_CFG_MAX_FILE_PATH 56
>  
> +#define VMCOREINFO_FORMAT_ELF 0x1
> +
>  /* platform device for dma mapping */
>  static struct device *dev;
>  
> @@ -127,7 +131,8 @@ static ssize_t fw_cfg_dma_transfer(void *address, u32 length, u32 control)
>  	dma_addr_t dma;
>  	ssize_t ret = length;
>  	enum dma_data_direction dir =
> -		(control & FW_CFG_DMA_CTL_READ ? DMA_FROM_DEVICE : 0);
> +		(control & FW_CFG_DMA_CTL_READ ? DMA_FROM_DEVICE : 0) |
> +		(control & FW_CFG_DMA_CTL_WRITE ? DMA_TO_DEVICE : 0);
>  
>  	if (address && length) {
>  		dma_addr = dma_map_single(dev, address, length, dir);
> @@ -225,6 +230,48 @@ static ssize_t fw_cfg_read_blob(u16 key,
>  	return ret;
>  }
>  
> +#ifdef CONFIG_CRASH_CORE
> +/* write chunk of given fw_cfg blob (caller responsible for sanity-check) */
> +static ssize_t fw_cfg_write_blob(u16 key,
> +				 void *buf, loff_t pos, size_t count)
> +{
> +	u32 glk = -1U;
> +	acpi_status status;
> +	ssize_t ret = count;
> +
> +	/* If we have ACPI, ensure mutual exclusion against any potential
> +	 * device access by the firmware, e.g. via AML methods:
> +	 */
> +	status = acpi_acquire_global_lock(ACPI_WAIT_FOREVER, &glk);
> +	if (ACPI_FAILURE(status) && status != AE_NOT_CONFIGURED) {
> +		/* Should never get here */
> +		WARN(1, "%s: Failed to lock ACPI!\n", __func__);
> +		memset(buf, 0, count);
> +		return -EINVAL;
> +	}
> +
> +	mutex_lock(&fw_cfg_dev_lock);
> +	if (pos == 0) {
> +		ret = fw_cfg_dma_transfer(buf, count, key << 16
> +					  | FW_CFG_DMA_CTL_SELECT
> +					  | FW_CFG_DMA_CTL_WRITE);
> +	} else {
> +		iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
> +		ret = fw_cfg_dma_transfer(NULL, pos, FW_CFG_DMA_CTL_SKIP);
> +		if (ret < 0)
> +			goto end;
> +		ret = fw_cfg_dma_transfer(buf, count, FW_CFG_DMA_CTL_WRITE);
> +	}
> +
> +end:
> +	mutex_unlock(&fw_cfg_dev_lock);
> +
> +	acpi_release_global_lock(glk);
> +
> +	return ret;
> +}
> +#endif /* CONFIG_CRASH_CORE */
> +
>  /* clean up fw_cfg device i/o */
>  static void fw_cfg_io_cleanup(void)
>  {
> @@ -343,6 +390,37 @@ struct fw_cfg_sysfs_entry {
>  	struct list_head list;
>  };
>  
> +#ifdef CONFIG_CRASH_CORE
> +static ssize_t write_vmcoreinfo(const struct fw_cfg_file *f)
> +{
> +	struct vmci {
> +		__le16 host_format;
> +		__le16 guest_format;
> +		__le32 size;
> +		__le64 paddr;
> +	} __packed;
> +	struct vmci *data;
> +	ssize_t ret;
> +
> +	data = kmalloc(sizeof(struct vmci), GFP_KERNEL | GFP_DMA);
> +	if (!data)
> +		return -ENOMEM;

It's a small bit of data - you can just keep it in a global variable,
this way failures won't be an issue.

> +
> +	/* spare ourself reading host format support for now since we
> +	 * don't know what else to format - host may ignore ours
> +	 */
> +	*data = (struct vmci) {
> +		.guest_format = cpu_to_le16(VMCOREINFO_FORMAT_ELF),
> +		.size = cpu_to_le32(VMCOREINFO_NOTE_SIZE),
> +		.paddr = cpu_to_le64(paddr_vmcoreinfo_note())
> +	};
> +	ret = fw_cfg_write_blob(f->select, data, 0, sizeof(struct vmci));
> +
> +	kfree(data);
> +	return ret;
> +}
> +#endif /* CONFIG_CRASH_CORE */
> +
>  /* get fw_cfg_sysfs_entry from kobject member */
>  static inline struct fw_cfg_sysfs_entry *to_entry(struct kobject *kobj)
>  {
> @@ -582,6 +660,13 @@ static int fw_cfg_register_file(const struct fw_cfg_file *f)
>  	int err;
>  	struct fw_cfg_sysfs_entry *entry;
>  
> +#ifdef CONFIG_CRASH_CORE
> +	if (strcmp(f->name, "etc/vmcoreinfo") == 0 && !is_kdump_kernel()) {
> +		if (write_vmcoreinfo(f) < 0)
> +			pr_warn("fw_cfg: failed to write vmcoreinfo");
> +	}
> +#endif
> +
>  	/* allocate new entry */
>  	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
>  	if (!entry)
> -- 
> 2.15.0.125.g8f49766d64

Hi

----- Original Message -----
> On Mon, Nov 13, 2017 at 08:29:58PM +0100, Marc-André Lureau wrote:
> > If the "etc/vmcoreinfo" fw_cfg file is present and we are not running
> > the kdump kernel, write the addr/size of the vmcoreinfo ELF note.
> > 
> > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > Reviewed-by: Gabriel Somlo <somlo@cmu.edu>
> > ---
> >  drivers/firmware/qemu_fw_cfg.c | 87
> >  +++++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 86 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/firmware/qemu_fw_cfg.c
> > b/drivers/firmware/qemu_fw_cfg.c
> > index 2ac4cd869fe6..7a70e7a549f6 100644
> > --- a/drivers/firmware/qemu_fw_cfg.c
> > +++ b/drivers/firmware/qemu_fw_cfg.c
> > @@ -35,6 +35,8 @@
> >  #include <linux/ioport.h>
> >  #include <linux/delay.h>
> >  #include <linux/dma-mapping.h>
> > +#include <linux/crash_core.h>
> > +#include <linux/crash_dump.h>
> >  
> >  MODULE_AUTHOR("Gabriel L. Somlo <somlo@cmu.edu>");
> >  MODULE_DESCRIPTION("QEMU fw_cfg sysfs support");
> > @@ -59,6 +61,8 @@ MODULE_LICENSE("GPL");
> >  /* fw_cfg "file name" is up to 56 characters (including terminating nul)
> >  */
> >  #define FW_CFG_MAX_FILE_PATH 56
> >  
> > +#define VMCOREINFO_FORMAT_ELF 0x1
> > +
> >  /* platform device for dma mapping */
> >  static struct device *dev;
> >  
> > @@ -127,7 +131,8 @@ static ssize_t fw_cfg_dma_transfer(void *address, u32
> > length, u32 control)
> >  	dma_addr_t dma;
> >  	ssize_t ret = length;
> >  	enum dma_data_direction dir =
> > -		(control & FW_CFG_DMA_CTL_READ ? DMA_FROM_DEVICE : 0);
> > +		(control & FW_CFG_DMA_CTL_READ ? DMA_FROM_DEVICE : 0) |
> > +		(control & FW_CFG_DMA_CTL_WRITE ? DMA_TO_DEVICE : 0);
> >  
> >  	if (address && length) {
> >  		dma_addr = dma_map_single(dev, address, length, dir);
> > @@ -225,6 +230,48 @@ static ssize_t fw_cfg_read_blob(u16 key,
> >  	return ret;
> >  }
> >  
> > +#ifdef CONFIG_CRASH_CORE
> > +/* write chunk of given fw_cfg blob (caller responsible for sanity-check)
> > */
> > +static ssize_t fw_cfg_write_blob(u16 key,
> > +				 void *buf, loff_t pos, size_t count)
> > +{
> > +	u32 glk = -1U;
> > +	acpi_status status;
> > +	ssize_t ret = count;
> > +
> > +	/* If we have ACPI, ensure mutual exclusion against any potential
> > +	 * device access by the firmware, e.g. via AML methods:
> > +	 */
> > +	status = acpi_acquire_global_lock(ACPI_WAIT_FOREVER, &glk);
> > +	if (ACPI_FAILURE(status) && status != AE_NOT_CONFIGURED) {
> > +		/* Should never get here */
> > +		WARN(1, "%s: Failed to lock ACPI!\n", __func__);
> > +		memset(buf, 0, count);
> > +		return -EINVAL;
> > +	}
> > +
> > +	mutex_lock(&fw_cfg_dev_lock);
> > +	if (pos == 0) {
> > +		ret = fw_cfg_dma_transfer(buf, count, key << 16
> > +					  | FW_CFG_DMA_CTL_SELECT
> > +					  | FW_CFG_DMA_CTL_WRITE);
> > +	} else {
> > +		iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
> > +		ret = fw_cfg_dma_transfer(NULL, pos, FW_CFG_DMA_CTL_SKIP);
> > +		if (ret < 0)
> > +			goto end;
> > +		ret = fw_cfg_dma_transfer(buf, count, FW_CFG_DMA_CTL_WRITE);
> > +	}
> > +
> > +end:
> > +	mutex_unlock(&fw_cfg_dev_lock);
> > +
> > +	acpi_release_global_lock(glk);
> > +
> > +	return ret;
> > +}
> > +#endif /* CONFIG_CRASH_CORE */
> > +
> >  /* clean up fw_cfg device i/o */
> >  static void fw_cfg_io_cleanup(void)
> >  {
> > @@ -343,6 +390,37 @@ struct fw_cfg_sysfs_entry {
> >  	struct list_head list;
> >  };
> >  
> > +#ifdef CONFIG_CRASH_CORE
> > +static ssize_t write_vmcoreinfo(const struct fw_cfg_file *f)
> > +{
> > +	struct vmci {
> > +		__le16 host_format;
> > +		__le16 guest_format;
> > +		__le32 size;
> > +		__le64 paddr;
> > +	} __packed;
> > +	struct vmci *data;
> > +	ssize_t ret;
> > +
> > +	data = kmalloc(sizeof(struct vmci), GFP_KERNEL | GFP_DMA);
> > +	if (!data)
> > +		return -ENOMEM;
> 
> It's a small bit of data - you can just keep it in a global variable,
> this way failures won't be an issue.

It would still need to be allocated with GFP_DMA. Since it's a one time thing, this is just moving the problem isn't it?

> 
> > +
> > +	/* spare ourself reading host format support for now since we
> > +	 * don't know what else to format - host may ignore ours
> > +	 */
> > +	*data = (struct vmci) {
> > +		.guest_format = cpu_to_le16(VMCOREINFO_FORMAT_ELF),
> > +		.size = cpu_to_le32(VMCOREINFO_NOTE_SIZE),
> > +		.paddr = cpu_to_le64(paddr_vmcoreinfo_note())
> > +	};
> > +	ret = fw_cfg_write_blob(f->select, data, 0, sizeof(struct vmci));
> > +
> > +	kfree(data);
> > +	return ret;
> > +}
> > +#endif /* CONFIG_CRASH_CORE */
> > +
> >  /* get fw_cfg_sysfs_entry from kobject member */
> >  static inline struct fw_cfg_sysfs_entry *to_entry(struct kobject *kobj)
> >  {
> > @@ -582,6 +660,13 @@ static int fw_cfg_register_file(const struct
> > fw_cfg_file *f)
> >  	int err;
> >  	struct fw_cfg_sysfs_entry *entry;
> >  
> > +#ifdef CONFIG_CRASH_CORE
> > +	if (strcmp(f->name, "etc/vmcoreinfo") == 0 && !is_kdump_kernel()) {
> > +		if (write_vmcoreinfo(f) < 0)
> > +			pr_warn("fw_cfg: failed to write vmcoreinfo");
> > +	}
> > +#endif
> > +
> >  	/* allocate new entry */
> >  	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
> >  	if (!entry)
> > --
> > 2.15.0.125.g8f49766d64
> 

On Thu, Nov 16, 2017 at 08:34:23AM -0500, Marc-André Lureau wrote:
> Hi
> 
> ----- Original Message -----
> > On Mon, Nov 13, 2017 at 08:29:58PM +0100, Marc-André Lureau wrote:
> > > If the "etc/vmcoreinfo" fw_cfg file is present and we are not running
> > > the kdump kernel, write the addr/size of the vmcoreinfo ELF note.
> > > 
> > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > Reviewed-by: Gabriel Somlo <somlo@cmu.edu>
> > > ---
> > >  drivers/firmware/qemu_fw_cfg.c | 87
> > >  +++++++++++++++++++++++++++++++++++++++++-
> > >  1 file changed, 86 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/firmware/qemu_fw_cfg.c
> > > b/drivers/firmware/qemu_fw_cfg.c
> > > index 2ac4cd869fe6..7a70e7a549f6 100644
> > > --- a/drivers/firmware/qemu_fw_cfg.c
> > > +++ b/drivers/firmware/qemu_fw_cfg.c
> > > @@ -35,6 +35,8 @@
> > >  #include <linux/ioport.h>
> > >  #include <linux/delay.h>
> > >  #include <linux/dma-mapping.h>
> > > +#include <linux/crash_core.h>
> > > +#include <linux/crash_dump.h>
> > >  
> > >  MODULE_AUTHOR("Gabriel L. Somlo <somlo@cmu.edu>");
> > >  MODULE_DESCRIPTION("QEMU fw_cfg sysfs support");
> > > @@ -59,6 +61,8 @@ MODULE_LICENSE("GPL");
> > >  /* fw_cfg "file name" is up to 56 characters (including terminating nul)
> > >  */
> > >  #define FW_CFG_MAX_FILE_PATH 56
> > >  
> > > +#define VMCOREINFO_FORMAT_ELF 0x1
> > > +
> > >  /* platform device for dma mapping */
> > >  static struct device *dev;
> > >  
> > > @@ -127,7 +131,8 @@ static ssize_t fw_cfg_dma_transfer(void *address, u32
> > > length, u32 control)
> > >  	dma_addr_t dma;
> > >  	ssize_t ret = length;
> > >  	enum dma_data_direction dir =
> > > -		(control & FW_CFG_DMA_CTL_READ ? DMA_FROM_DEVICE : 0);
> > > +		(control & FW_CFG_DMA_CTL_READ ? DMA_FROM_DEVICE : 0) |
> > > +		(control & FW_CFG_DMA_CTL_WRITE ? DMA_TO_DEVICE : 0);
> > >  
> > >  	if (address && length) {
> > >  		dma_addr = dma_map_single(dev, address, length, dir);
> > > @@ -225,6 +230,48 @@ static ssize_t fw_cfg_read_blob(u16 key,
> > >  	return ret;
> > >  }
> > >  
> > > +#ifdef CONFIG_CRASH_CORE
> > > +/* write chunk of given fw_cfg blob (caller responsible for sanity-check)
> > > */
> > > +static ssize_t fw_cfg_write_blob(u16 key,
> > > +				 void *buf, loff_t pos, size_t count)
> > > +{
> > > +	u32 glk = -1U;
> > > +	acpi_status status;
> > > +	ssize_t ret = count;
> > > +
> > > +	/* If we have ACPI, ensure mutual exclusion against any potential
> > > +	 * device access by the firmware, e.g. via AML methods:
> > > +	 */
> > > +	status = acpi_acquire_global_lock(ACPI_WAIT_FOREVER, &glk);
> > > +	if (ACPI_FAILURE(status) && status != AE_NOT_CONFIGURED) {
> > > +		/* Should never get here */
> > > +		WARN(1, "%s: Failed to lock ACPI!\n", __func__);
> > > +		memset(buf, 0, count);
> > > +		return -EINVAL;
> > > +	}
> > > +
> > > +	mutex_lock(&fw_cfg_dev_lock);
> > > +	if (pos == 0) {
> > > +		ret = fw_cfg_dma_transfer(buf, count, key << 16
> > > +					  | FW_CFG_DMA_CTL_SELECT
> > > +					  | FW_CFG_DMA_CTL_WRITE);
> > > +	} else {
> > > +		iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
> > > +		ret = fw_cfg_dma_transfer(NULL, pos, FW_CFG_DMA_CTL_SKIP);
> > > +		if (ret < 0)
> > > +			goto end;
> > > +		ret = fw_cfg_dma_transfer(buf, count, FW_CFG_DMA_CTL_WRITE);
> > > +	}
> > > +
> > > +end:
> > > +	mutex_unlock(&fw_cfg_dev_lock);
> > > +
> > > +	acpi_release_global_lock(glk);
> > > +
> > > +	return ret;
> > > +}
> > > +#endif /* CONFIG_CRASH_CORE */
> > > +
> > >  /* clean up fw_cfg device i/o */
> > >  static void fw_cfg_io_cleanup(void)
> > >  {
> > > @@ -343,6 +390,37 @@ struct fw_cfg_sysfs_entry {
> > >  	struct list_head list;
> > >  };
> > >  
> > > +#ifdef CONFIG_CRASH_CORE
> > > +static ssize_t write_vmcoreinfo(const struct fw_cfg_file *f)
> > > +{
> > > +	struct vmci {
> > > +		__le16 host_format;
> > > +		__le16 guest_format;
> > > +		__le32 size;
> > > +		__le64 paddr;
> > > +	} __packed;
> > > +	struct vmci *data;
> > > +	ssize_t ret;
> > > +
> > > +	data = kmalloc(sizeof(struct vmci), GFP_KERNEL | GFP_DMA);
> > > +	if (!data)
> > > +		return -ENOMEM;
> > 
> > It's a small bit of data - you can just keep it in a global variable,
> > this way failures won't be an issue.
> 
> It would still need to be allocated

No - you can just make it a global variable.

> with GFP_DMA.

Are you sure?

 * GFP_DMA exists for historical reasons and should be avoided where possible.
 *   The flags indicates that the caller requires that the lowest zone be
 *   used (ZONE_DMA or 16M on x86-64). Ideally, this would be removed but
 *   it would require careful auditing as some users really require it and
 *   others use the flag to avoid lowmem reserves in ZONE_DMA and treat the
 *   lowest zone as a type of emergency reserve.


> Since it's a one time thing, this is just moving the problem isn't it?

Isn't the timeout just moving the problem too?
Avoiding memory corruption is a priority.

> > 
> > > +
> > > +	/* spare ourself reading host format support for now since we
> > > +	 * don't know what else to format - host may ignore ours
> > > +	 */
> > > +	*data = (struct vmci) {
> > > +		.guest_format = cpu_to_le16(VMCOREINFO_FORMAT_ELF),
> > > +		.size = cpu_to_le32(VMCOREINFO_NOTE_SIZE),
> > > +		.paddr = cpu_to_le64(paddr_vmcoreinfo_note())
> > > +	};
> > > +	ret = fw_cfg_write_blob(f->select, data, 0, sizeof(struct vmci));
> > > +
> > > +	kfree(data);
> > > +	return ret;
> > > +}
> > > +#endif /* CONFIG_CRASH_CORE */
> > > +
> > >  /* get fw_cfg_sysfs_entry from kobject member */
> > >  static inline struct fw_cfg_sysfs_entry *to_entry(struct kobject *kobj)
> > >  {
> > > @@ -582,6 +660,13 @@ static int fw_cfg_register_file(const struct
> > > fw_cfg_file *f)
> > >  	int err;
> > >  	struct fw_cfg_sysfs_entry *entry;
> > >  
> > > +#ifdef CONFIG_CRASH_CORE
> > > +	if (strcmp(f->name, "etc/vmcoreinfo") == 0 && !is_kdump_kernel()) {
> > > +		if (write_vmcoreinfo(f) < 0)
> > > +			pr_warn("fw_cfg: failed to write vmcoreinfo");
> > > +	}
> > > +#endif
> > > +
> > >  	/* allocate new entry */
> > >  	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
> > >  	if (!entry)
> > > --
> > > 2.15.0.125.g8f49766d64
> >