Re: [RFC PATCH] firmware: qemu_fw_cfg.c: hold ACPI global lock during device access
From: Greg KH <hidden>
Date: 2016-03-08 00:02:22
Also in:
linux-devicetree, lkml, qemu-devel
On Mon, Mar 07, 2016 at 06:55:43PM -0500, Gabriel Somlo wrote:
quoted hunk ↗ jump to hunk
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 <redacted> Signed-off-by: Gabriel Somlo <somlo-D+Gtc/HYRWM@public.gmane.org> --- Turns out, there *is* a way to acquire a global ACPI lock from within a "random" kernel driver after all. Luckily I have a healthy dose of respect for Michael's opinions :) so I kept circling back through existing kernel sources for an example I can use, and I think this might be it. I'm posting as RFC because I'm not really confident about assessing the likelihood of there ever being a race condition between the kernel fw_cfg sysfs driver and firmware on my own. Obviously Michael has concerns about it, but any additional opinions from the QEMU camp would be much appreciated. Thanks again, --Gabriel drivers/firmware/qemu_fw_cfg.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c index 7bba76c..cc4c27a 100644 --- a/drivers/firmware/qemu_fw_cfg.c +++ b/drivers/firmware/qemu_fw_cfg.c@@ -77,12 +77,26 @@ 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) { +#ifdef CONFIG_ACPI + u32 glk; + int status; + status = acpi_acquire_global_lock(ACPI_WAIT_FOREVER, &glk);
Why not fix up the ACPI api to not require #ifdef here? It should be added to a .h file somewhere instead.
+ if (ACPI_FAILURE(status)) {
+ /* Should never get here */
+ WARN(1, "fw_cfg_read_blob: Failed to lock ACPI!\n");
+ memset(buf, 0, count);
+ return;
+ }
+#endif
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);
+#ifdef CONFIG_ACPI
+ acpi_release_global_lock(glk);Same here. thanks, greg k-h