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firmware: qemu_fw_cfg.c: hold ACPI global lock during device access 

Allowing for the future possibility of implementing AML-based
(i.e., firmware-triggered) access to the QEMU fw_cfg device,
acquire the global ACPI lock when accessing the device on behalf
of the guest-side sysfs driver, to prevent any potential race
conditions.

Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Gabriel Somlo 2016-03-08 13:30:50 -05:00 committed by Michael S. Tsirkin
parent 05dbcb4307
commit def7ac806a
1 changed files with 16 additions and 0 deletions
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16
drivers/firmware/qemu_fw_cfg.c
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@ -77,12 +77,28 @@ static inline u16 fw_cfg_sel_endianness(u16 key)
static inline void fw_cfg_read_blob(u16 key,
void *buf, loff_t pos, size_t count)
{
u32 glk;
acpi_status status;
/* 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, "fw_cfg_read_blob: Failed to lock ACPI!\n");
memset(buf, 0, count);
return;
}
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);
mutex_unlock(&fw_cfg_dev_lock);
acpi_release_global_lock(glk);
}
/* clean up fw_cfg device i/o */