Re: [PATCH v14 8/9] fw_cfg: write vmcoreinfo details

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Feb 15, 2018 at 07:24:34PM +0100, Marc-André Lureau wrote:
> Hi
> 
> On Thu, Feb 15, 2018 at 7:09 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> > On Wed, Feb 14, 2018 at 03:18:49PM +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@redhat.com>
> >> ---
> >>  drivers/firmware/qemu_fw_cfg.c | 144 ++++++++++++++++++++++++++++++++++++++++-
> >>  1 file changed, 141 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
> >> index 37638b95cb45..69939e2529f2 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 <linux/fw_cfg.h>
> >> +#include <linux/delay.h>
> >> +#include <linux/crash_dump.h>
> >> +#include <linux/crash_core.h>
> >>
> >>  MODULE_AUTHOR("Gabriel L. Somlo <somlo@cmu.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;
> >> @@ -59,6 +65,65 @@ static inline u16 fw_cfg_sel_endianness(u16 key)
> >>               (u16 __force)cpu_to_le16(key);
> >>  }
> >>
> >> +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)
> >> +{
> >> +     do {
> >> +             u32 ctrl = be32_to_cpu(READ_ONCE(d->control));
> >> +
> >> +             if ((ctrl & ~FW_CFG_DMA_CTL_ERROR) == 0)
> >> +                     return;
> >> +
> >> +             usleep_range(50, 100);
> >
> > I would just do cpu_relax() here.
> 
> ok, I didn't know that one.
> 
> >
> >> +     } while (true);

Pls write for (;;) and not do - while (true).

> >> +
> >> +     /* do not reorder the read to d->control */
> >> +     rmb();
> >
> > Hmm. I don't really understand the comment.
> > Is this code ever reacheable? How does it help?
> 
> I thought that's what you suggested in v13 review, but true, I should
> replace the return with a break to reach it. Is that what you expect
> too?

I'd do it unconditionally after reading ctrl.

> (my understanding is to make sure the READ_ONCE(control) in
> wait_for_control happens before READ_ONCE(control) after in
> dma_transfer)

I expect you to understand memory-barriers.txt :)

> >
> >> +}
> >> +
> >> +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 inline void fw_cfg_read_blob(u16 key,
> >>                                   void *buf, loff_t pos, size_t count)
> >> @@ -87,6 +152,47 @@ static inline void fw_cfg_read_blob(u16 key,
> >>       acpi_release_global_lock(glk);
> >>  }
> >>
> >> +#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 {
> >> +             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)
> >>  {
> >> @@ -185,9 +291,6 @@ 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);
> >> @@ -210,6 +313,32 @@ 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
> >> +      */
> >> +     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)
> >>  {
> >> @@ -450,6 +579,15 @@ 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)
> >> --
> >> 2.16.1.73.g5832b7e9f2