Date:   Tue, 27 Feb 2018 02:28:29 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Marc-André Lureau <marcandre.lureau@...hat.com>
Cc:     linux-kernel@...r.kernel.org, slp@...hat.com, bhe@...hat.com,
        somlo@....edu, xiaolong.ye@...el.com
Subject: Re: [PATCH v15 10/11] fw_cfg: write vmcoreinfo details

On Thu, Feb 15, 2018 at 10:33:11PM +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.
> 
> The DMA operation is expected to run synchronously with today qemu,
> but the specification states that it may become async, so we run
> "control" field check in a loop for eventual changes.
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@...hat.com>
> ---
>  drivers/firmware/qemu_fw_cfg.c | 143 ++++++++++++++++++++++++++++++++++++++++-
>  include/uapi/linux/fw_cfg.h    |  31 +++++++++
>  2 files changed, 171 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
> index c28bec4b5663..3015e77aebca 100644
> --- a/drivers/firmware/qemu_fw_cfg.c
> +++ b/drivers/firmware/qemu_fw_cfg.c
> @@ -34,11 +34,17 @@
>  #include <linux/io.h>
>  #include <linux/ioport.h>
>  #include <uapi/linux/fw_cfg.h>
> +#include <linux/delay.h>
> +#include <linux/crash_dump.h>
> +#include <linux/crash_core.h>
>  
>  MODULE_AUTHOR("Gabriel L. Somlo <somlo@....edu>");
>  MODULE_DESCRIPTION("QEMU fw_cfg sysfs support");
>  MODULE_LICENSE("GPL");
>  
> +/* fw_cfg revision attribute, in /sys/firmware/qemu_fw_cfg top-level dir. */
> +static u32 fw_cfg_rev;
> +
>  /* fw_cfg device i/o register addresses */
>  static bool fw_cfg_is_mmio;
>  static phys_addr_t fw_cfg_p_base;
> @@ -60,6 +66,64 @@ static void fw_cfg_sel_endianness(u16 key)
>  		iowrite16(key, fw_cfg_reg_ctrl);
>  }
>  
> +static inline bool fw_cfg_dma_enabled(void)
> +{
> +	return (fw_cfg_rev & FW_CFG_VERSION_DMA) && fw_cfg_reg_dma;
> +}
> +
> +/* qemu fw_cfg device is sync today, but spec says it may become async */
> +static void fw_cfg_wait_for_control(struct fw_cfg_dma_access *d)
> +{
> +	for (;;) {
> +		u32 ctrl = be32_to_cpu(READ_ONCE(d->control));
> +
> +		/* do not reorder the read to d->control */
> +		rmb();
> +		if ((ctrl & ~FW_CFG_DMA_CTL_ERROR) == 0)
> +			return;
> +
> +		cpu_relax();
> +	}
> +}
> +
> +static ssize_t fw_cfg_dma_transfer(void *address, u32 length, u32 control)
> +{
> +	phys_addr_t dma;
> +	struct fw_cfg_dma_access *d = NULL;
> +	ssize_t ret = length;
> +
> +	d = kmalloc(sizeof(*d), GFP_KERNEL);
> +	if (!d) {
> +		ret = -ENOMEM;
> +		goto end;
> +	}
> +
> +	/* fw_cfg device does not need IOMMU protection, so use physical addresses */
> +	*d = (struct fw_cfg_dma_access) {
> +		.address = cpu_to_be64(address ? virt_to_phys(address) : 0),
> +		.length = cpu_to_be32(length),
> +		.control = cpu_to_be32(control)
> +	};
> +
> +	dma = virt_to_phys(d);
> +
> +	iowrite32be((u64)dma >> 32, fw_cfg_reg_dma);
> +	/* force memory to sync before notifying device via MMIO */
> +	wmb();
> +	iowrite32be(dma, fw_cfg_reg_dma + 4);
> +
> +	fw_cfg_wait_for_control(d);
> +
> +	if (be32_to_cpu(READ_ONCE(d->control)) & FW_CFG_DMA_CTL_ERROR) {
> +		ret = -EIO;
> +	}
> +
> +end:
> +	kfree(d);
> +
> +	return ret;
> +}
> +
>  /* read chunk of given fw_cfg blob (caller responsible for sanity-check) */
>  static ssize_t fw_cfg_read_blob(u16 key,
>  				void *buf, loff_t pos, size_t count)
> @@ -89,6 +153,47 @@ static ssize_t fw_cfg_read_blob(u16 key,
>  	return count;
>  }
>  
> +#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__);
> +		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 {
> +		fw_cfg_sel_endianness(key);
> +		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)
>  {
> @@ -188,9 +293,6 @@ static int fw_cfg_do_platform_probe(struct platform_device *pdev)
>  	return 0;
>  }
>  
> -/* fw_cfg revision attribute, in /sys/firmware/qemu_fw_cfg top-level dir. */
> -static u32 fw_cfg_rev;
> -
>  static ssize_t fw_cfg_showrev(struct kobject *k, struct attribute *a, char *buf)
>  {
>  	return sprintf(buf, "%u\n", fw_cfg_rev);
> @@ -213,6 +315,32 @@ struct fw_cfg_sysfs_entry {
>  	struct list_head list;
>  };
>  
> +#ifdef CONFIG_CRASH_CORE
> +static ssize_t fw_cfg_write_vmcoreinfo(const struct fw_cfg_file *f)
> +{
> +	static struct fw_cfg_vmcoreinfo *data;
> +	ssize_t ret;
> +
> +	data = kmalloc(sizeof(struct fw_cfg_vmcoreinfo), GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	*data = (struct fw_cfg_vmcoreinfo) {
> +		.guest_format = cpu_to_le16(FW_CFG_VMCOREINFO_FORMAT_ELF),
> +		.size = cpu_to_le32(VMCOREINFO_NOTE_SIZE),
> +		.paddr = cpu_to_le64(paddr_vmcoreinfo_note())
> +	};
> +	/* spare ourself reading host format support for now since we
> +	 * don't know what else to format - host may ignore ours


qemu documentation probably should mention that it must.

> +	 */
> +	ret = fw_cfg_write_blob(be16_to_cpu(f->select), data,
> +				0, sizeof(struct fw_cfg_vmcoreinfo));
> +
> +	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)
>  {
> @@ -452,6 +580,15 @@ 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 (fw_cfg_dma_enabled() &&
> +		strcmp(f->name, FW_CFG_VMCOREINFO_FILENAME) == 0 &&
> +		!is_kdump_kernel()) {
> +		if (fw_cfg_write_vmcoreinfo(f) < 0)
> +			pr_warn("fw_cfg: failed to write vmcoreinfo");
> +	}
> +#endif
> +
>  	/* allocate new entry */
>  	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
>  	if (!entry)
> diff --git a/include/uapi/linux/fw_cfg.h b/include/uapi/linux/fw_cfg.h
> index c698ac3812f6..e089c0159ec2 100644
> --- a/include/uapi/linux/fw_cfg.h
> +++ b/include/uapi/linux/fw_cfg.h
> @@ -54,6 +54,7 @@
>  
>  /* FW_CFG_ID bits */
>  #define FW_CFG_VERSION		0x01
> +#define FW_CFG_VERSION_DMA	0x02
>  
>  /* fw_cfg file directory entry type */
>  struct fw_cfg_file {
> @@ -63,4 +64,34 @@ struct fw_cfg_file {
>  	char name[FW_CFG_MAX_FILE_PATH];
>  };
>  
> +/* FW_CFG_DMA_CONTROL bits */
> +#define FW_CFG_DMA_CTL_ERROR	0x01
> +#define FW_CFG_DMA_CTL_READ	0x02
> +#define FW_CFG_DMA_CTL_SKIP	0x04
> +#define FW_CFG_DMA_CTL_SELECT	0x08
> +#define FW_CFG_DMA_CTL_WRITE	0x10
> +
> +#define FW_CFG_DMA_SIGNATURE    0x51454d5520434647ULL /* "QEMU CFG" */
> +
> +/* Control as first field allows for different structures selected by this
> + * field, which might be useful in the future
> + */
> +struct fw_cfg_dma_access {
> +	__be32 control;
> +	__be32 length;
> +	__be64 address;
> +};
> +
> +#define FW_CFG_VMCOREINFO_FILENAME "etc/vmcoreinfo"
> +
> +#define FW_CFG_VMCOREINFO_FORMAT_NONE 0x0
> +#define FW_CFG_VMCOREINFO_FORMAT_ELF 0x1
> +
> +struct fw_cfg_vmcoreinfo {
> +	__le16 host_format;
> +	__le16 guest_format;
> +	__le32 size;
> +	__le64 paddr;
> +};
> +
>  #endif
> -- 
> 2.16.1.73.g5832b7e9f2

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