From def7ac806a9ac035abf0e7573ccc8bbfd38e163c Mon Sep 17 00:00:00 2001 From: Gabriel Somlo Date: Tue, 8 Mar 2016 13:30:50 -0500 Subject: [PATCH] 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 Signed-off-by: Gabriel Somlo Signed-off-by: Michael S. Tsirkin --- 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 e4c4714..815c4a5 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 */ -- 2.7.4