On Wed, 2019-07-10 at 05:20:18 UTC, Suraj Jitindar Singh wrote: > The virtual real mode addressing (VRMA) mechanism is used when a > partition is using HPT (Hash Page Table) translation and performs > real mode accesses (MSR[IR|DR] = 0) in non-hypervisor mode. In this > mode effective address bits 0:23 are treated as zero (i.e. the access > is aliased to 0) and the access is performed using an implicit 1TB SLB > entry. > > The size of the RMA (Real Memory Area) is communicated to the guest as > the size of the first memory region in the device tree. And because of > the mechanism described above can be expected to not exceed 1TB. In the > event that the host erroneously represents the RMA as being larger than > 1TB, guest accesses in real mode to memory addresses above 1TB will be > aliased down to below 1TB. This means that a memory access performed in > real mode may differ to one performed in virtual mode for the same memory > address, which would likely have unintended consequences. > > To avoid this outcome have the guest explicitly limit the size of the > RMA to the current maximum, which is 1TB. This means that even if the > first memory block is larger than 1TB, only the first 1TB should be > accessed in real mode. > > Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx> > Tested-by: Satheesh Rajendran <sathnaga@xxxxxxxxxxxxxxxxxx> > Reviewed-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> Applied to powerpc fixes, thanks. https://git.kernel.org/powerpc/c/da0ef93310e67ae6902efded60b6724dab27a5d1 cheers
