Re: [PATCH v6 5/5] fw_cfg: write vmcoreinfo details

[Michael S. Tsirkin]

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@xxxxxxxxxx>
> Reviewed-by: Gabriel Somlo <somlo@xxxxxxx>
> ---
>  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@xxxxxxx>");
>  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