[PATCH] powerpc: mm: Limit rma_size to 1TB when running without HV mode

[Michael Ellerman]

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 at gmail.com>
> Tested-by: Satheesh Rajendran <sathnaga at linux.vnet.ibm.com>
> Reviewed-by: David Gibson <david at gibson.dropbear.id.au>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/da0ef93310e67ae6902efded60b6724dab27a5d1

cheers