Ross Philipson wrote on 2013-04-30: > We have been looking at the code in tboot.c that sets the tboot memory > area to E820_UNUSABLE when it detects that the next module is not Linux. > Specifically this code: > > uint32_t mem_type = is_kernel_linux() ? E820_RESERVED : E820_UNUSABLE; > > And this commit: > > http://hg.code.sf.net/p/tboot/code/rev/b170b7b39e5c > > It seems to make sense to set the region to reserved but we do not > understand why the region is set to unusable in the other case. Can > someone explain the reasoning behind this?
> > Also, the check for is_kernel_linux() relies on it not being an elf > image but this doesn't seem very correct. Not being an elf image does > not imply it is a Linux kernel. Are you relying on the fact that only > Linux and Xen are used with tboot at the moment? > > Thanks, > Ross Philipson In ACPI spec: AddressRangeReserved defined as: This range of addresses is in use or reserved by the system and is not to be included in the allocatable memory pool of the operating system's memory manager. AddressRangeUnusable: This range of addresses contains memory in which errors have been detected. This range must not be used by OSPM. Only Unusable AddressRange is forbidden to be used by OS. So we set tboot memory as E820_UNUSABLE for both Linux kernel & Xen cases in the beginning. But in Linux case, we then found some issues so we had to reset the type to RESERVED to fix that issue. That is all I can recall now. As to the check for is_kernel_linux(), yes, we currently only support Xen & Linux kernel, so we just differentiate them by the elf property. It might need to be changed in the future. Jimmy
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