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Message-ID: <20180214214105-mutt-send-email-mst@kernel.org>
Date: Thu, 15 Feb 2018 20:09:58 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Marc-André Lureau <marcandre.lureau@...hat.com>
Cc: linux-kernel@...r.kernel.org, bhe@...hat.com, slp@...hat.com,
somlo@....edu, xiaolong.ye@...el.com
Subject: Re: [PATCH v14 8/9] fw_cfg: write vmcoreinfo details
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@...hat.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@....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.
> + } 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?
> +}
> +
> +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
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