On 02/12/19 at 10:37am, Bhupesh Sharma wrote: > Hi Kazu, > > On 02/04/2019 09:34 PM, Kazuhito Hagio wrote: > > On 1/30/2019 8:48 PM, Dave Young wrote: > > > + more people > > > On 01/30/19 at 05:53pm, Bhupesh Sharma wrote: > > > > With ARMv8.2-LVA and LPA architecture extensions, arm64 hardware which > > > > supports these extensions can support upto 52-bit virtual and 52-bit > > > > physical addresses respectively. > > > > > > > > Since at the moment we enable the support of these extensions via CONFIG > > > > flags, e.g. > > > > - LPA via CONFIG_ARM64_PA_BITS_52 > > > > > > > > there are no clear mechanisms in user-space right now to > > > > deteremine these CONFIG flag values and also determine the PARange and > > > > VARange address values. > > > > > > > > User-space tools like 'makedumpfile' and 'crash-utility' can instead > > > > use the 'MAX_USER_VA_BITS' and 'MAX_PHYSMEM_BITS' values to determine > > > > the maximum virtual address and physical address (respectively) > > > > supported by underlying kernel. > > > > > > > > A reference 'makedumpfile' implementation which uses this approach to > > > > determining the maximum physical address is available in [0]. > > > > > > > > [0]. > > > https://github.com/bhupesh-sharma/makedumpfile/blob/52-bit-pa-support-via-vmcore-v1/arch/arm64.c#L490 > > > > > > I'm not objecting the patch, just want to make sure to make clear about > > > things and make sure these issues are aware by people, and leave arm > > > people to review the arm bits. > > > > > > 1. MAX_PHYSMEM_BITS > > > As we previously found, back to 2014 makedumpfile took a patch to read the > > > value from vmcore but the kernel patch was not accepted. > > > So we should first make clear if this is really needed, why other arches > > > do not need this in makedumpfile. > > > > > > If we really need it then should it be arm64 only? > > > > > > If it is arm64 only then the makedumpfile code should read this number > > > only for arm64. > > > > Sorry for the delay. > > > > According to the kernel patch, some of arm32 platforms may need it > > http://lists.infradead.org/pipermail/kexec/2014-May/011909.html > > but except for them (and arm64), makedumpfile can manage with kernel > > version and some switches to determine this value so far. > > > > > > > > Also Lianbo added the vmcoreinfo documents, I believe it stays in -tip > > > tree, need to make sure to document this as well. > > > > > > 2. MAX_USER_VA_BITS > > > Does makedumpfile care about userspace VA bits? I do not see other code > > > doing this, Kazu and Dave A should be able to comment. > > > > The mapping makedumpfile uses on arm64 is swapper_pg_dir only, so > > unless the config affects its structure or something, makedumpfile > > will not need this value. > > I captured this case in more details while sending out the makedumpfile > enablement patch for ARMv8.2-LVA (see [0]), but here is a brief summary on > the same: > > Since at the moment we enable the support of the ARMv8.2-LVA extension for > 52-bit user-space VA in the kernel via a CONFIG flags > (CONFIG_ARM64_USER_VA_BITS_52), so there are no clear mechanisms in > user-space to determine this CONFIG > flag value and use it to determine the address range values. > > Since 'VA_BITS' are already exported via vmcoreinfo, if we export > 'MAX_USER_VA_BITS' as well, we can use the same in user-space to check if > the 'MAX_USER_VA_BITS' value is greater than 'VA_BITS'. If yes, then we are > running a use-case where user-space is 52-bit while the underlying kernel is > still 48-bit. Problem is why this is needed, it sounds like you are talking about some non-exist use case. > > The increased 'PTRS_PER_PGD' value for such cases needs to be then > calculated as is done by the underlying kernel (see > 'arch/arm64/include/asm/pgtable-hwdef.h' for details): > > #define PTRS_PER_PGD (1 << (MAX_USER_VA_BITS - PGDIR_SHIFT)) > > Also, note that 'arch/arm64/include/asm/memory.h' defines 'MAX_USER_VA_BITS' > as 'VA_BITS' in case 'CONFIG_ARM64_USER_VA_BITS_52' is set to 'n': > > #ifdef CONFIG_ARM64_USER_VA_BITS_52 > #define MAX_USER_VA_BITS 52 > #else > #define MAX_USER_VA_BITS VA_BITS > #endif > > So, makedumpfile will need this symbol exported in vmcore to make the above > determination. > > [0]. http://lists.infradead.org/pipermail/kexec/2019-February/022425.html > > Thanks, > Bhupesh Thanks Dave _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
