Re: [RFC PATCH v1 00/57] Boot-time page size selection for arm64

Petr Tesarik
2024-10-24T11:52:33Z

On Thu, 24 Oct 2024 11:48:55 +0100
Ryan Roberts <ryan.roberts@arm.com> wrote:

> On 23/10/2024 22:00, Thomas Tai wrote:
> >
> > On 10/17/2024 8:32 AM, Ryan Roberts wrote:
> >> On 17/10/2024 13:27, Petr Tesarik wrote:
> >>> On Mon, 14 Oct 2024 11:55:11 +0100
> >>> Ryan Roberts <ryan.roberts@arm.com> wrote:
> >>>
> >>>> [...]
> >>>> The series is arranged as follows:
> >>>>
> >>>>    - patch 1:       Add macros required for converting non-arch code to support
> >>>>               boot-time page size selection
> >>>>    - patches 2-36:  Remove PAGE_SIZE compile-time constant assumption from all
> >>>>               non-arch code
> >>> I have just tried to recompile the openSUSE kernel with these patches
> >>> applied, and I'm running into this:
> >>>
> >>>    CC      arch/arm64/hyperv/hv_core.o
> >>> In file included from ../arch/arm64/hyperv/hv_core.c:14:0:
> >>> ../include/linux/hyperv.h:158:5: error: variably modified ‘reserved2’ at file
> >>> scope
> >>>    u8 reserved2[PAGE_SIZE - 68];
> >>>       ^~~~~~~~~
> >>>
> >>> It looks like one more place which needs a patch, right?
> >> As mentioned in the cover letter, so far I've only converted enough to get the
> >> defconfig *image* building (i.e. no modules). If you are compiling a different
> >> config or compiling the modules for defconfig, you will likely run into these
> >> types of issues.
> >
> > It would be nice if you could provide the defconfig you are using; I also ran
> > into build issues when using the arch/arm64/configs/defconfig.
>
> git clean -xdfq
> make defconfig
>
> # Set CONFIG_ARM64_BOOT_TIME_PAGE_SIZE
> ./scripts/config --disable CONFIG_ARM64_4K_PAGES
> ./scripts/config --disable CONFIG_ARM64_16K_PAGES
> ./scripts/config --disable CONFIG_ARM64_64K_PAGES
> ./scripts/config --disable CONFIG_ARM64_BOOT_TIME_PAGE_SIZE
> ./scripts/config --enable CONFIG_ARM64_BOOT_TIME_PAGE_SIZE
>
> # Set ARM64_VA_BITS_48
> ./scripts/config --disable ARM64_VA_BITS_36
> ./scripts/config --disable ARM64_VA_BITS_39
> ./scripts/config --disable ARM64_VA_BITS_42
> ./scripts/config --disable ARM64_VA_BITS_47
> ./scripts/config --disable ARM64_VA_BITS_48
> ./scripts/config --disable ARM64_VA_BITS_52
> ./scripts/config --enable ARM64_VA_BITS_48
>
> # Optional: filesystems known to compile with boot-time page size
> ./scripts/config --enable CONFIG_SQUASHFS_LZ4
> ./scripts/config --enable CONFIG_SQUASHFS_LZO
> ./scripts/config --enable CONFIG_SQUASHFS_XZ
> ./scripts/config --enable CONFIG_SQUASHFS_ZSTD
> ./scripts/config --enable CONFIG_XFS_FS
>
> # Optional: trace stuff known to compile with boot-time page size
> ./scripts/config --enable CONFIG_FTRACE
> ./scripts/config --enable CONFIG_FUNCTION_TRACER
> ./scripts/config --enable CONFIG_KPROBES
> ./scripts/config --enable CONFIG_HIST_TRIGGERS
> ./scripts/config --enable CONFIG_FTRACE_SYSCALLS
>
> # Optional: misc mm stuff known to compile with boot-time page size
> ./scripts/config --enable CONFIG_PTDUMP_DEBUGFS
> ./scripts/config --enable CONFIG_READ_ONLY_THP_FOR_FS
> ./scripts/config --enable CONFIG_USERFAULTFD
>
> # Optional: mm debug stuff known compile with boot-time page size
> ./scripts/config --enable CONFIG_DEBUG_VM
> ./scripts/config --enable CONFIG_DEBUG_VM_MAPLE_TREE
> ./scripts/config --enable CONFIG_DEBUG_VM_RB
> ./scripts/config --enable CONFIG_DEBUG_VM_PGFLAGS
> ./scripts/config --enable CONFIG_DEBUG_VM_PGTABLE
> ./scripts/config --enable CONFIG_PAGE_TABLE_CHECK
> ./scripts/config --enable CONFIG_PAGE_TABLE_CHECK_ENFORCED
>
> make olddefconfig
> make -s -j`nproc` Image
>
> So I'm explicitly only building and booting the kernel image, not the modules.
> The kernel image contains all the drivers needed to get a VM up and running
> under QEMU/KVM.

FWIW with the attached patch I was also able to boot the kernel on
Ampere Altra bare metal and using modules.

Petr T

diff --git a/arch/arm64/mm/pgtable-geometry.c b/arch/arm64/mm/pgtable-geometry.c
index ba50637f1e9d..4eb074b99654 100644
--- a/arch/arm64/mm/pgtable-geometry.c
+++ b/arch/arm64/mm/pgtable-geometry.c
@@ -15,8 +15,14 @@
*/

int ptg_page_shift __read_mostly;
+EXPORT_SYMBOL_GPL(ptg_page_shift);
+
int ptg_pmd_shift __read_mostly;
+EXPORT_SYMBOL_GPL(ptg_pmd_shift);
+
int ptg_pud_shift __read_mostly;
+EXPORT_SYMBOL_GPL(ptg_pud_shift);
+
int ptg_p4d_shift __read_mostly;
int ptg_pgdir_shift __read_mostly;
int ptg_cont_pte_shift __read_mostly;