My 2 cents > -----Original Message----- > From: arm.ebbr-discuss-boun...@arm.com [mailto:arm.ebbr-discuss- > boun...@arm.com] On Behalf Of Grant Likely > Sent: Thursday, July 12, 2018 4:11 PM > To: boot-architecture@lists.linaro.org; arm.ebbr-disc...@arm.com > Cc: n...@arm.com > Subject: [Arm.ebbr-discuss] [RFC] uefi: Account for SetVariable() not working > at > runtime > > Add details on what to do if the platform is unable to set persistent > variables in > runtime services. The idea here is that the GetVariable() and SetVariable() > APIs > should continue to work, and the OS can obtain all the variable settings, but > if it > cannot be written then the NON_VOLATILE attribute is cleared so the OS knows > that persistence is not available. > > Cc: Dong Wei <dong....@arm.com> > Cc: Alexander Graf <ag...@suse.de> > Cc: Peter Robinson <pbrobin...@redhat.com> > Signed-off-by: Grant Likely <grant.lik...@arm.com> > --- > > Alex/Peter: Does this approach work for you? I tried to come up with something > that is faithful to the spec, gives the OS information that non-volatile > variables > aren't available, but still have the ability to query the boot environment. > > Dong: Is this an appropriate way to use {Get,Set}Variable()? > > Cheers, > g. > > --- > source/chapter2-uefi.rst | 18 +++++++++--------- > 1 file changed, 9 insertions(+), 9 deletions(-) > > diff --git a/source/chapter2-uefi.rst b/source/chapter2-uefi.rst index > 7b6843e..57594bc 100644 > --- a/source/chapter2-uefi.rst > +++ b/source/chapter2-uefi.rst > @@ -197,13 +197,13 @@ command: > Operating Systems calls to reset the system will go via Runtime Services > and not directly to PSCI. > > -Set Variable > ------------- > - > -Non-volatile UEFI variables must persist across reset, and emulated > variables - > in RAM are not permitted. > -The UEFI Runtime Services must be able to update the variables directly > without > -the aid of the Operating System. > +Runtime Variable Access > +----------------------- > > -.. note:: This normally requires dedicated storage for UEFI variables that is > - not directly accessible from the Operating System. > +Non-volatile UEFI variables must persist across reset. > +If the platform is incapable of updating non-volatile variables from > +Runtime Services then it must clear the EFI_VARIABLE_NON_VOLATILE > +attribute from all non-volatile variables when ExitBootServices() is called.
This is really good statement for specification. I believe this will solve the problem of shared storage too. > +Similarly, if non-volatile variables cannot be set from Runtime > +Services, then > +SetVariable() must return EFI_INVALID_PARAMETER if the > +EFI_VARIABLE_NON_VOLATILE attribute is set. You meant EFI_VARIABLE_NON_VOLATILE is reset ? Also I am not sure, if UEFI specs says return error EFI_INVALID_PARAMETER if variable is volatile Can we add statement for GetVariable too, UEFI Specs says " Variables that have runtime access but that are not nonvolatile are read-only data variables once ExitBootServices() is performed." So this means, firmware (edk2 or u-boot) needs to take care of this. Simply caching variables in RAM could solve the purpose as SetVariable is not allowed. > -- > 2.13.0 > > _______________________________________________ > Arm.ebbr-discuss mailing list > arm.ebbr-disc...@arm.com _______________________________________________ boot-architecture mailing list boot-architecture@lists.linaro.org https://lists.linaro.org/mailman/listinfo/boot-architecture
