Hi Julien, > -----Original Message----- > From: Xen-devel <[email protected]> On Behalf Of > Julien Grall > Sent: 2023年1月18日 19:00 > To: Wei Chen <[email protected]>; Penny Zheng <[email protected]>; xen- > [email protected] > Cc: Stefano Stabellini <[email protected]>; Bertrand Marquis > <[email protected]>; Volodymyr Babchuk <[email protected]>; > Jiamei Xie <[email protected]> > Subject: Re: [PATCH v2 04/40] xen/arm: add an option to define Xen start > address for Armv8-R > > Hi, > > On 18/01/2023 10:22, Wei Chen wrote: > >>> Although it is unlikely that vendors using the Armv8-R IP will do so, > it > >>> is indeed an option. In the ID register, there are also related bits > in > >>> ID_AA64MMFR0_EL1 (MSA_frac) to indicate this. > >>> > >>>>> --- > >>>>> xen/arch/arm/Kconfig | 8 ++++++++ > >>>>> xen/arch/arm/platforms/Kconfig | 16 +++++++++++++--- > >>>>> 2 files changed, 21 insertions(+), 3 deletions(-) > >>>>> > >>>>> diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig > >>>>> index ace7178c9a..c6b6b612d1 100644 > >>>>> --- a/xen/arch/arm/Kconfig > >>>>> +++ b/xen/arch/arm/Kconfig > >>>>> @@ -145,6 +145,14 @@ config TEE > >>>>> This option enables generic TEE mediators support. It allows > >>>> guests > >>>>> to access real TEE via one of TEE mediators implemented in > >> XEN. > >>>>> > >>>>> +config XEN_START_ADDRESS > >>>>> + hex "Xen start address: keep default to use platform defined > >>>> address" > >>>>> + default 0 > >>>>> + depends on ARM_V8R > >>>> > >>>> It is still pretty unclear to me what would be the difference between > >>>> HAS_MPU and ARM_V8R. > >>>> > >>> > >>> If we don't want to support non-MPU supported Armv8-R, I think they > are > >> the > >>> same. IMO, non-MPU supported Armv8-R is meaningless to Xen. > >> OOI, why do you think this is meaningless? > > > > If there is Armv8-R board without EL2 MPU, how can we protect Xen? > > So what you call EL2 MPU is an MPU that is following the Arm > specification. In theory, you could have a proprietary mechanism for that. > > So the question is whether a system not following the Arm specification > is allowed. >
I think no, the PMSA is an architectural feature, the spec contains CPU and MPU interfaces. Vendors can have their own hardware implementation, but need follow the Arm spec. But I agree that, here we could change to "depends on HAS_MPU" which will make It easier to used by other Arm Architecture or other architecture in the future. Cheers, Wei Chen > Cheers, > > -- > Julien Grall
