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Re: [Qemu-devel] [PATCH v7 3/5] fw_cfg: do DMA read operation


From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH v7 3/5] fw_cfg: do DMA read operation
Date: Mon, 20 Nov 2017 23:49:32 +0200

On Mon, Nov 20, 2017 at 10:55:17AM +0100, Marc-André Lureau wrote:
> Modify fw_cfg_read_blob() to use DMA if the device supports it.
> Return errors, because the operation may fail.
> 
> 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.
> 
> We may want to switch all the *buf addresses to use only kmalloc'ed
> buffers (instead of using stack/image addresses with dma=false).
> 
> Signed-off-by: Marc-André Lureau <address@hidden>
> ---
>  drivers/firmware/qemu_fw_cfg.c | 140 
> ++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 123 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
> index 740df0df2260..e0fe6ff037c3 100644
> --- a/drivers/firmware/qemu_fw_cfg.c
> +++ b/drivers/firmware/qemu_fw_cfg.c
> @@ -33,6 +33,8 @@
>  #include <linux/slab.h>
>  #include <linux/io.h>
>  #include <linux/ioport.h>
> +#include <linux/delay.h>
> +#include <linux/dma-mapping.h>
>  
>  MODULE_AUTHOR("Gabriel L. Somlo <address@hidden>");
>  MODULE_DESCRIPTION("QEMU fw_cfg sysfs support");
> @@ -43,12 +45,25 @@ MODULE_LICENSE("GPL");
>  #define FW_CFG_ID         0x01
>  #define FW_CFG_FILE_DIR   0x19
>  
> +#define FW_CFG_VERSION_DMA     0x02
> +#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
> +
>  /* size in bytes of fw_cfg signature */
>  #define FW_CFG_SIG_SIZE 4
>  
>  /* fw_cfg "file name" is up to 56 characters (including terminating nul) */
>  #define FW_CFG_MAX_FILE_PATH 56
>  
> +/* platform device for dma mapping */
> +static struct device *dev;
> +
> +/* fw_cfg revision attribute, in /sys/firmware/qemu_fw_cfg top-level dir. */
> +static u32 fw_cfg_rev;
> +
>  /* fw_cfg file directory entry type */
>  struct fw_cfg_file {
>       u32 size;
> @@ -57,6 +72,12 @@ struct fw_cfg_file {
>       char name[FW_CFG_MAX_FILE_PATH];
>  };
>  
> +struct fw_cfg_dma {
> +     u32 control;
> +     u32 length;
> +     u64 address;
> +} __packed;
> +
>  /* fw_cfg device i/o register addresses */
>  static bool fw_cfg_is_mmio;
>  static phys_addr_t fw_cfg_p_base;

Drop __packed please. It causes many gcc versions to do insane things.
Can be a patch on top.


> @@ -75,12 +96,79 @@ static inline u16 fw_cfg_sel_endianness(u16 key)
>       return fw_cfg_is_mmio ? cpu_to_be16(key) : 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 *d, dma_addr_t dma)
> +{
> +     do {
> +             dma_sync_single_for_cpu(dev, dma, sizeof(*d), DMA_FROM_DEVICE);
> +             if ((be32_to_cpu(d->control) & ~FW_CFG_DMA_CTL_ERROR) == 0)
> +                     return;
> +
> +             usleep_range(50, 100);

And since in practice we never get to this line,
maybe we should just go back to yield here.

> +     } while (true);
> +}
> +
> +static ssize_t fw_cfg_dma_transfer(void *address, u32 length, u32 control)
> +{
> +     dma_addr_t dma_addr = 0;
> +     static struct fw_cfg_dma d;
> +     dma_addr_t dma;
> +     ssize_t ret = length;
> +     enum dma_data_direction dir =
> +             (control & FW_CFG_DMA_CTL_READ ? DMA_FROM_DEVICE : 0);
> +
> +     if (address && length) {
> +             dma_addr = dma_map_single(dev, address, length, dir);
> +             if (dma_mapping_error(NULL, dma_addr)) {
> +                     WARN(1, "%s: failed to map address\n", __func__);
> +                     return -EFAULT;
> +             }
> +     }
> +
> +     d = (struct fw_cfg_dma) {
> +             .address = cpu_to_be64(dma_addr),
> +             .length = cpu_to_be32(length),
> +             .control = cpu_to_be32(control)
> +     };
> +
> +     dma = dma_map_single(dev, &d, sizeof(d), DMA_BIDIRECTIONAL);
> +     if (dma_mapping_error(NULL, dma)) {
> +             WARN(1, "%s: failed to map fw_cfg_dma\n", __func__);
> +             ret = -EFAULT;
> +             goto end;
> +     }
> +
> +     iowrite32be((u64)dma >> 32, fw_cfg_reg_dma);
> +     iowrite32be(dma, fw_cfg_reg_dma + 4);
> +
> +     fw_cfg_wait_for_control(&d, dma);
> +
> +     if (be32_to_cpu(d.control) & FW_CFG_DMA_CTL_ERROR) {
> +             ret = -EIO;
> +     }
> +
> +     dma_unmap_single(dev, dma, sizeof(d), DMA_BIDIRECTIONAL);
> +
> +end:
> +     if (dma_addr)
> +             dma_unmap_single(dev, dma_addr, length, dir);
> +
> +     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)
> +static ssize_t fw_cfg_read_blob(u16 key,
> +                             void *buf, loff_t pos, size_t count,
> +                             bool dma)
>  {
>       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:
> @@ -90,17 +178,36 @@ static inline void fw_cfg_read_blob(u16 key,
>               /* Should never get here */
>               WARN(1, "fw_cfg_read_blob: Failed to lock ACPI!\n");
>               memset(buf, 0, count);
> -             return;
> +             return -EINVAL;
>       }
>  
>       mutex_lock(&fw_cfg_dev_lock);
> -     iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
> -     while (pos-- > 0)
> -             ioread8(fw_cfg_reg_data);
> -     ioread8_rep(fw_cfg_reg_data, buf, count);
> +     if (dma && fw_cfg_dma_enabled()) {
> +             if (pos == 0) {
> +                     ret = fw_cfg_dma_transfer(buf, count, key << 16
> +                                               | FW_CFG_DMA_CTL_SELECT
> +                                               | FW_CFG_DMA_CTL_READ);
> +             } 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_READ);
> +             }
> +     } else {
> +             iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
> +             while (pos-- > 0)
> +                     ioread8(fw_cfg_reg_data);
> +             ioread8_rep(fw_cfg_reg_data, buf, count);
> +     }
> +
> +end:
>       mutex_unlock(&fw_cfg_dev_lock);
>  
>       acpi_release_global_lock(glk);
> +
> +     return ret;
>  }
>  
>  /* clean up fw_cfg device i/o */
> @@ -192,7 +299,7 @@ static int fw_cfg_do_platform_probe(struct 
> platform_device *pdev)
>  #endif
>  
>       /* verify fw_cfg device signature */
> -     fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, 0, FW_CFG_SIG_SIZE);
> +     fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, 0, FW_CFG_SIG_SIZE, false);
>       if (memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) {
>               fw_cfg_io_cleanup();
>               return -ENODEV;
> @@ -201,9 +308,6 @@ 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);
> @@ -351,8 +455,7 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, 
> struct kobject *kobj,
>       if (count > entry->f.size - pos)
>               count = entry->f.size - pos;
>  
> -     fw_cfg_read_blob(entry->f.select, buf, pos, count);
> -     return count;
> +     return fw_cfg_read_blob(entry->f.select, buf, pos, count, true);
>  }
>  
>  static struct bin_attribute fw_cfg_sysfs_attr_raw = {
> @@ -505,7 +608,7 @@ static int fw_cfg_register_dir_entries(void)
>       struct fw_cfg_file *dir;
>       size_t dir_size;
>  
> -     fw_cfg_read_blob(FW_CFG_FILE_DIR, &count, 0, sizeof(count));
> +     fw_cfg_read_blob(FW_CFG_FILE_DIR, &count, 0, sizeof(count), false);
>       count = be32_to_cpu(count);
>       dir_size = count * sizeof(struct fw_cfg_file);
>  
> @@ -513,7 +616,7 @@ static int fw_cfg_register_dir_entries(void)
>       if (!dir)
>               return -ENOMEM;
>  
> -     fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, sizeof(count), dir_size);
> +     fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, sizeof(count), dir_size, true);
>  
>       for (i = 0; i < count; i++) {
>               dir[i].size = be32_to_cpu(dir[i].size);
> @@ -544,9 +647,10 @@ static int fw_cfg_sysfs_probe(struct platform_device 
> *pdev)
>        * one fw_cfg device exist system-wide, so if one was already found
>        * earlier, we might as well stop here.
>        */
> -     if (fw_cfg_sel_ko)
> +     if (dev)
>               return -EBUSY;
>  
> +     dev = &pdev->dev;
>       /* create by_key and by_name subdirs of /sys/firmware/qemu_fw_cfg/ */
>       err = -ENOMEM;
>       fw_cfg_sel_ko = kobject_create_and_add("by_key", fw_cfg_top_ko);
> @@ -562,7 +666,7 @@ static int fw_cfg_sysfs_probe(struct platform_device 
> *pdev)
>               goto err_probe;
>  
>       /* get revision number, add matching top-level attribute */
> -     fw_cfg_read_blob(FW_CFG_ID, &fw_cfg_rev, 0, sizeof(fw_cfg_rev));
> +     fw_cfg_read_blob(FW_CFG_ID, &fw_cfg_rev, 0, sizeof(fw_cfg_rev), false);
>       fw_cfg_rev = le32_to_cpu(fw_cfg_rev);
>       err = sysfs_create_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr);
>       if (err)
> @@ -587,6 +691,7 @@ static int fw_cfg_sysfs_probe(struct platform_device 
> *pdev)
>  err_name:
>       fw_cfg_kobj_cleanup(fw_cfg_sel_ko);
>  err_sel:
> +     dev = NULL;
>       return err;
>  }
>  
> @@ -598,6 +703,7 @@ static int fw_cfg_sysfs_remove(struct platform_device 
> *pdev)
>       fw_cfg_io_cleanup();
>       fw_cfg_kset_unregister_recursive(fw_cfg_fname_kset);
>       fw_cfg_kobj_cleanup(fw_cfg_sel_ko);
> +     dev = NULL;
>       return 0;
>  }
>  
> -- 
> 2.15.0.277.ga3d2ad2c43



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