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Date: Thu, 15 Feb 2018 19:24:34 +0100
From: Marc-André Lureau <marcandre.lureau@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Baoquan He <bhe@...hat.com>,
Sergio Lopez Pascual <slp@...hat.com>,
"Somlo, Gabriel" <somlo@....edu>, xiaolong.ye@...el.com
Subject: Re: [PATCH v14 8/9] fw_cfg: write vmcoreinfo details
Hi
On Thu, Feb 15, 2018 at 7:09 PM, Michael S. Tsirkin <mst@...hat.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@...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.
ok, I didn't know that one.
>
>> + } 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? (my understanding is to make sure the READ_ONCE(control) in
wait_for_control happens before READ_ONCE(control) after in
dma_transfer)
>
>> +}
>> +
>> +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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