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 <m...@redhat.com>
Signed-off-by: Gabriel Somlo <so...@cmu.edu>
---
Changes since v1:
- no more "#ifdef CONFIG_ACPI"; instead we proceed if
acpi_acquire_global_lock() returns either OK or NOT_CONFIGURED,
and only throw a warning/error message otherwise.
- didn't get any *negative* feedback from the QEMU crowd, so
this is now a bona-fide "please apply this", rather than just
an RFC :)
- tested on ACPI-enabled x86_64, and acpi_less ARM (32 and 64 bit)
QEMU VMs (I don't have handy access to an ACPI-enabled ARM VM)
Thanks much,
--Gabriel
drivers/firmware/qemu_fw_cfg.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
index 7bba76c..a44dc32 100644
--- a/drivers/firmware/qemu_fw_cfg.c
+++ b/drivers/firmware/qemu_fw_cfg.c
@@ -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 */
--
2.4.3
