Date:   Mon, 12 Feb 2018 11:04:49 +0100
From:   Marc-Andre Lureau <mlureau@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Marc-André Lureau <marcandre.lureau@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sergio Lopez Pascual <slp@...hat.com>,
        Baoquan He <bhe@...hat.com>, "Somlo, Gabriel" <somlo@....edu>,
        xiaolong.ye@...el.com
Subject: Re: [PATCH v13 3/4] fw_cfg: write vmcoreinfo details

Hi

On Mon, Feb 12, 2018 at 4:43 AM, Michael S. Tsirkin <mst@...hat.com> wrote:
> On Wed, Feb 07, 2018 at 02:35:24AM +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 | 157 ++++++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 154 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
>> index 740df0df2260..fd576ba7b337 100644
>> --- a/drivers/firmware/qemu_fw_cfg.c
>> +++ b/drivers/firmware/qemu_fw_cfg.c
>> @@ -33,6 +33,9 @@
>>  #include <linux/slab.h>
>>  #include <linux/io.h>
>>  #include <linux/ioport.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");
>> @@ -43,12 +46,24 @@ 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
>>
>> +#define VMCOREINFO_FORMAT_ELF 0x1
>
> How about exporting interface parts in include/uapi/linux/ ?
> QEMU can import it from there then.
> This is what virtio does.

Good idea, we didn't have it yet. So this is an additional change.
I'll work on it. Though, if this should delay more this series, I
think we should drop it.

>
>> +
>> +/* 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;
>> +
>
> you can drop __packed here - it's always aligned properly.

Isn't it preferable to make that explicit? Fwiw, qemu also declares
the struct packed in its headers.

>
>>  /* fw_cfg device i/o register addresses */
>>  static bool fw_cfg_is_mmio;
>>  static phys_addr_t fw_cfg_p_base;
>> @@ -75,6 +96,59 @@ 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;
>
> Why do you use () with == below but not with && here?
>

Let's add them.

>> +}
>> +
>> +/* 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)
>> +{
>> +     do {
>> +             u32 ctrl = be32_to_cpu(READ_ONCE(d->control));
>> +
>> +             if ((ctrl & ~FW_CFG_DMA_CTL_ERROR) == 0)
>> +                     return;
>> +
>> +             usleep_range(50, 100);
>> +     } while (true);
>
> And you need an smp rmb here.

Could you explain? thanks

>
>> +}
>> +
>> +static ssize_t fw_cfg_dma_transfer(void *address, u32 length, u32 control)
>> +{
>> +     phys_addr_t dma;
>> +     struct fw_cfg_dma *d = NULL;
>> +     ssize_t ret = length;
>> +
>> +     d = kmalloc(sizeof(*d), GFP_KERNEL);
>> +     if (!d) {
>> +             ret = -ENOMEM;
>> +             goto end;
>> +     }
>> +
>> +     *d = (struct fw_cfg_dma) {
>> +             .address = address ? cpu_to_be64(virt_to_phys(address)) : 0,
>> +             .length = cpu_to_be32(length),
>> +             .control = cpu_to_be32(control)
>> +     };
>> +
>> +     dma = virt_to_phys(d);
>
> Pls add docs on why this DMA bypasses the DMA API.

Peter said in his patch: "fw_cfg device does not need IOMMU
protection, so use physical addresses
always.  That's how QEMU implements fw_cfg.  Otherwise we'll see call
traces during boot."

Is that enough justification?

>
>> +
>> +     iowrite32be((u64)dma >> 32, fw_cfg_reg_dma);
>> +     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)
>> @@ -103,6 +177,47 @@ 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)
>
> fw_cfg_dma_write seems like a nicer name.

ok (I used the same naming as fw_cfg_read_blob() for consistency)

>
>> +{
>> +     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)
>>  {
>> @@ -201,9 +316,6 @@ 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);
>> @@ -224,6 +336,37 @@ struct fw_cfg_sysfs_entry {
>>       struct list_head list;
>>  };
>>
>> +#ifdef CONFIG_CRASH_CORE
>> +static ssize_t write_vmcoreinfo(const struct fw_cfg_file *f)
>
> why not prefix with fw_cfg here?

ok

>
>> +{
>> +     struct vmci {
>> +             __le16 host_format;
>> +             __le16 guest_format;
>> +             __le32 size;
>> +             __le64 paddr;
>> +     } __packed;
>
>
> No need for the __packed attribute.

discussed above

> And pls do not declare structures within functions.
> Name them sanely and place in a header or near top of file.

ok

>
>> +     static struct vmci *data;
>> +     ssize_t ret;
>> +
>> +     data = kmalloc(sizeof(struct vmci), GFP_KERNEL);
>> +     if (!data)
>> +             return -ENOMEM;
>> +
>> +     *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())
>> +     };
>> +     /* 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(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)
>>  {
>> @@ -464,6 +607,14 @@ 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, "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)
>> --
>> 2.16.1.73.g5832b7e9f2

thanks

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