From: Suraj Jitindar Singh sjitindarsingh@gmail.com
commit da0ef93310e67ae6902efded60b6724dab27a5d1 upstream.
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.
Fixes: c610d65c0ad0 ("powerpc/pseries: lift RTAS limit for hash") Cc: stable@vger.kernel.org # v4.16+ Signed-off-by: Suraj Jitindar Singh sjitindarsingh@gmail.com Tested-by: Satheesh Rajendran sathnaga@linux.vnet.ibm.com Reviewed-by: David Gibson david@gibson.dropbear.id.au Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20190710052018.14628-1-sjitindarsingh@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/mm/book3s64/hash_utils.c | 9 +++++++++ 1 file changed, 9 insertions(+)
--- a/arch/powerpc/mm/book3s64/hash_utils.c +++ b/arch/powerpc/mm/book3s64/hash_utils.c @@ -1901,11 +1901,20 @@ void hash__setup_initial_memory_limit(ph * * For guests on platforms before POWER9, we clamp the it limit to 1G * to avoid some funky things such as RTAS bugs etc... + * + * On POWER9 we limit to 1TB in case the host erroneously told us that + * the RMA was >1TB. Effective address bits 0:23 are treated as zero + * (meaning the access is aliased to zero i.e. addr = addr % 1TB) + * for virtual real mode addressing and so it doesn't make sense to + * have an area larger than 1TB as it can't be addressed. */ if (!early_cpu_has_feature(CPU_FTR_HVMODE)) { ppc64_rma_size = first_memblock_size; if (!early_cpu_has_feature(CPU_FTR_ARCH_300)) ppc64_rma_size = min_t(u64, ppc64_rma_size, 0x40000000); + else + ppc64_rma_size = min_t(u64, ppc64_rma_size, + 1UL << SID_SHIFT_1T);
/* Finally limit subsequent allocations */ memblock_set_current_limit(ppc64_rma_size);