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

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