Hi Conor, On Mon, Jan 23, 2023 at 11:11 PM Conor Dooley <conor@xxxxxxxxxx> wrote: > > On Mon, Jan 23, 2023 at 12:28:02PM +0100, Alexandre Ghiti wrote: > > During the early page table creation, we used to set the mapping for > > PAGE_OFFSET to the kernel load address: but the kernel load address is > > always offseted by PMD_SIZE which makes it impossible to use PUD/P4D/PGD > > pages as this physical address is not aligned on PUD/P4D/PGD size (whereas > > PAGE_OFFSET is). > > > > But actually we don't have to establish this mapping (ie set va_pa_offset) > > that early in the boot process because: > > > > - first, setup_vm installs a temporary kernel mapping and among other > > things, discovers the system memory, > > - then, setup_vm_final creates the final kernel mapping and takes > > advantage of the discovered system memory to create the linear > > mapping. > > > > During the first phase, we don't know the start of the system memory and > > then until the second phase is finished, we can't use the linear mapping at > > all and phys_to_virt/virt_to_phys translations must not be used because it > > would result in a different translation from the 'real' one once the final > > mapping is installed. > > > > So here we simply delay the initialization of va_pa_offset to after the > > system memory discovery. But to make sure noone uses the linear mapping > > before, we add some guard in the DEBUG_VIRTUAL config. > > > > Finally we can use PUD/P4D/PGD hugepages when possible, which will result > > in a better TLB utilization. > > > > Note that we rely on the firmware to protect itself using PMP. > > > > Acked-by: Rob Herring <robh@xxxxxxxxxx> # DT bits > > Signed-off-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> > > No good on !MMU unfortunately Alex: > ../arch/riscv/mm/init.c:222:2: error: use of undeclared identifier 'riscv_pfn_base' > riscv_pfn_base = PFN_DOWN(phys_ram_base); > ^ > > Reproduces with nommu_virt_defconfig. Thanks, fixed locally, I'll push the v5 soon. Thanks again, Alex > > Thanks, > Conor.
