| Message ID | 20160307235543.GD2049@HEDWIG.INI.CMU.EDU (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, Mar 07, 2016 at 06:55:43PM -0500, Gabriel Somlo wrote: > 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> > --- > > 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
On Mon, Mar 07, 2016 at 04:02:15PM -0800, Greg KH wrote: > On Mon, Mar 07, 2016 at 06:55:43PM -0500, Gabriel Somlo wrote: > > 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> ACK, except for Gerd's comments below. > > --- > > > > 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 You should include linux/acpi.h if you use this, do not rely on some other header to pull this in. > > + 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. Indeed. In fact include/acpi/platform/aclinux.h already has this code: #ifndef CONFIG_ACPI /* External globals for __KERNEL__, stubs is needed */ #define ACPI_GLOBAL(t,a) #define ACPI_INIT_GLOBAL(t,a,b) /* Generating stubs for configurable ACPICA macros */ #define ACPI_NO_MEM_ALLOCATIONS /* Generating stubs for configurable ACPICA functions */ #define ACPI_NO_ERROR_MESSAGES #undef ACPI_DEBUG_OUTPUT /* External interface for __KERNEL__, stub is needed */ #define ACPI_EXTERNAL_RETURN_STATUS(prototype) \ static ACPI_INLINE prototype {return(AE_NOT_CONFIGURED);} #define ACPI_EXTERNAL_RETURN_OK(prototype) \ static ACPI_INLINE prototype {return(AE_OK);} #define ACPI_EXTERNAL_RETURN_VOID(prototype) \ static ACPI_INLINE prototype {return;} #define ACPI_EXTERNAL_RETURN_UINT32(prototype) \ static ACPI_INLINE prototype {return(0);} #define ACPI_EXTERNAL_RETURN_PTR(prototype) \ static ACPI_INLINE prototype {return(NULL);} #endif /* CONFIG_ACPI */ so it's just a question of testing the return code for AE_NOT_CONFIGURED.
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); + 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); +#endif } /* clean up fw_cfg device i/o */
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> --- 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(+)