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Commit def7ac80 authored by Gabriel Somlo's avatar Gabriel Somlo Committed by Michael S. Tsirkin
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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: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarGabriel Somlo <somlo@cmu.edu>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 05dbcb43

drivers/firmware/qemu_fw_cfg.c

+16 −0
Original line number Diff line number Diff line
@@ -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 */