Details about Low-Address Protection can be found in description of patch 1 and 2. It is basically a subpage protection of the first two pages of every address space (for which it is enabled).
We can achieve this by simply directly invalidating the TLB entry and therefore forcing every write accesses onto these two pages into the slow path. With this patch, I can boot Linux just fine (which uses LAP). This also makes all related kvm-unit-tests that we have pass. The checks are working that good, that I discovered a STFL bug. STFL stores into the low addresses but low-address protection does explicitly not apply. The Linux kernel calls STFL while LAP is active. So without patch nr 3, booting Linux will fail. (this change is also part of a patch of my SMP series). Based on: https://github.com/cohuck/qemu.git s390-next Available on: https://github.com/dhildenb/qemu.git s390x_lap David Hildenbrand (3): accel/tcg: allow to invalidate a write TLB entry immediately s390x/tcg: low-address protection support s390x/tcg: make STFL store into the lowcore accel/tcg/cputlb.c | 5 ++- accel/tcg/softmmu_template.h | 4 +- include/exec/cpu-all.h | 3 ++ target/s390x/excp_helper.c | 3 +- target/s390x/helper.h | 2 +- target/s390x/mem_helper.c | 8 ---- target/s390x/misc_helper.c | 7 +++- target/s390x/mmu_helper.c | 96 ++++++++++++++++++++++++++++---------------- 8 files changed, 78 insertions(+), 50 deletions(-) -- 2.13.5
