On 12/13/22 00:02, 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. > > Signed-off-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> > --- > > v3: > - Change the comment about initrd_start VA conversion so that it fits > ARM64 and RISCV64 (and others in the future if needed), as suggested > by Rob > > v2: > - Add a comment on why RISCV64 does not need to set initrd_start/end that > early in the boot process, as asked by Rob > > Note that this patch is rebased on top of: > [PATCH v1 1/1] riscv: mm: call best_map_size many times during linear-mapping > > arch/riscv/include/asm/page.h | 16 ++++++++++++++++ > arch/riscv/mm/init.c | 25 +++++++++++++++++++------ > arch/riscv/mm/physaddr.c | 16 ++++++++++++++++ > drivers/of/fdt.c | 11 ++++++----- > 4 files changed, 57 insertions(+), 11 deletions(-) This works nicely on D1! Before: MemTotal: 490680 kB after: MemTotal: 492472 kB and I tested booting with CONFIG_DEBUG_VIRTUAL without issue as well. Reviewed-by: Samuel Holland <samuel@xxxxxxxxxxxx> Tested-by: Samuel Holland <samuel@xxxxxxxxxxxx>
