Hi Ryan, On Mon, 14 Oct 2024 at 13:02, Ryan Roberts <ryan.roberts@xxxxxxx> wrote: > > When boot-time page size is in operation, TRAMP_VALIAS is no longer a > compile-time constant, because the VA of a fixmap slot depends upon > PAGE_SIZE. > > Let's handle this by instead exporting the slot index, > FIX_ENTRY_TRAMP_BEGIN,to assembly, then do the TRAMP_VALIAS calculation > per page size and use alternatives to decide which variant to activate. > > Note that for the tramp_map_kernel case, we are one instruction short of > space in the vector to have NOPs for all 3 page size variants. So we do > if/else for 16K/64K and branch around it for the 4K case. This saves 2 > instructions. > > Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> > --- > > ***NOTE*** > Any confused maintainers may want to read the cover note here for context: > https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@xxxxxxx/ > > arch/arm64/kernel/asm-offsets.c | 2 +- > arch/arm64/kernel/entry.S | 50 ++++++++++++++++++++++++++------- > 2 files changed, 41 insertions(+), 11 deletions(-) > > diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c > index f32b8d7f00b2a..c45fa3e281884 100644 > --- a/arch/arm64/kernel/asm-offsets.c > +++ b/arch/arm64/kernel/asm-offsets.c > @@ -172,7 +172,7 @@ int main(void) > DEFINE(ARM64_FTR_SYSVAL, offsetof(struct arm64_ftr_reg, sys_val)); > BLANK(); > #ifdef CONFIG_UNMAP_KERNEL_AT_EL0 > - DEFINE(TRAMP_VALIAS, TRAMP_VALIAS); > + DEFINE(FIX_ENTRY_TRAMP_BEGIN, FIX_ENTRY_TRAMP_BEGIN); > #endif > #ifdef CONFIG_ARM_SDE_INTERFACE > DEFINE(SDEI_EVENT_INTREGS, offsetof(struct sdei_registered_event, interrupted_regs)); > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index 7ef0e127b149f..ba47dc8672c04 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -101,11 +101,27 @@ > .org .Lventry_start\@ + 128 // Did we overflow the ventry slot? > .endm > > +#define TRAMP_VALIAS(page_shift) (FIXADDR_TOP - (FIX_ENTRY_TRAMP_BEGIN << (page_shift))) > + > .macro tramp_alias, dst, sym > - .set .Lalias\@, TRAMP_VALIAS + \sym - .entry.tramp.text > - movz \dst, :abs_g2_s:.Lalias\@ > - movk \dst, :abs_g1_nc:.Lalias\@ > - movk \dst, :abs_g0_nc:.Lalias\@ > +alternative_if ARM64_USE_PAGE_SIZE_4K > + .set .Lalias4k\@, TRAMP_VALIAS(ARM64_PAGE_SHIFT_4K) + \sym - .entry.tramp.text > + movz \dst, :abs_g2_s:.Lalias4k\@ > + movk \dst, :abs_g1_nc:.Lalias4k\@ > + movk \dst, :abs_g0_nc:.Lalias4k\@ > +alternative_else_nop_endif > +alternative_if ARM64_USE_PAGE_SIZE_16K > + .set .Lalias16k\@, TRAMP_VALIAS(ARM64_PAGE_SHIFT_16K) + \sym - .entry.tramp.text > + movz \dst, :abs_g2_s:.Lalias16k\@ > + movk \dst, :abs_g1_nc:.Lalias16k\@ > + movk \dst, :abs_g0_nc:.Lalias16k\@ > +alternative_else_nop_endif > +alternative_if ARM64_USE_PAGE_SIZE_64K > + .set .Lalias64k\@, TRAMP_VALIAS(ARM64_PAGE_SHIFT_64K) + \sym - .entry.tramp.text > + movz \dst, :abs_g2_s:.Lalias64k\@ > + movk \dst, :abs_g1_nc:.Lalias64k\@ > + movk \dst, :abs_g0_nc:.Lalias64k\@ > +alternative_else_nop_endif Since you're changing these, might as well drop the middle movk as the fixmap is now always in the top 2 GiB of the VA space. However, wouldn't it be better to reuse the existing callback alternative stuff that Marc added for KVM? Same applies below, I reckon. > .endm > > /* > @@ -627,16 +643,30 @@ SYM_CODE_END(ret_to_user) > bic \tmp, \tmp, #USER_ASID_FLAG > msr ttbr1_el1, \tmp > #ifdef CONFIG_QCOM_FALKOR_ERRATUM_1003 > -alternative_if ARM64_WORKAROUND_QCOM_FALKOR_E1003 > +alternative_if_not ARM64_WORKAROUND_QCOM_FALKOR_E1003 > + b .Lskip_falkor_e1003\@ > +alternative_else_nop_endif > /* ASID already in \tmp[63:48] */ > - movk \tmp, #:abs_g2_nc:(TRAMP_VALIAS >> 12) > - movk \tmp, #:abs_g1_nc:(TRAMP_VALIAS >> 12) > - /* 2MB boundary containing the vectors, so we nobble the walk cache */ > - movk \tmp, #:abs_g0_nc:((TRAMP_VALIAS & ~(SZ_2M - 1)) >> 12) > +alternative_if ARM64_USE_PAGE_SIZE_4K > + movk \tmp, #:abs_g2_nc:(TRAMP_VALIAS(ARM64_PAGE_SHIFT_4K) >> 12) > + movk \tmp, #:abs_g1_nc:(TRAMP_VALIAS(ARM64_PAGE_SHIFT_4K) >> 12) > + movk \tmp, #:abs_g0_nc:((TRAMP_VALIAS(ARM64_PAGE_SHIFT_4K) & ~(SZ_2M - 1)) >> 12) > + b .Lfinish_falkor_e1003\@ > +alternative_else_nop_endif > +alternative_if ARM64_USE_PAGE_SIZE_16K > + movk \tmp, #:abs_g2_nc:(TRAMP_VALIAS(ARM64_PAGE_SHIFT_16K) >> 12) > + movk \tmp, #:abs_g1_nc:(TRAMP_VALIAS(ARM64_PAGE_SHIFT_16K) >> 12) > + movk \tmp, #:abs_g0_nc:((TRAMP_VALIAS(ARM64_PAGE_SHIFT_16K) & ~(SZ_2M - 1)) >> 12) > +alternative_else /* ARM64_USE_PAGE_SIZE_64K */ > + movk \tmp, #:abs_g2_nc:(TRAMP_VALIAS(ARM64_PAGE_SHIFT_64K) >> 12) > + movk \tmp, #:abs_g1_nc:(TRAMP_VALIAS(ARM64_PAGE_SHIFT_64K) >> 12) > + movk \tmp, #:abs_g0_nc:((TRAMP_VALIAS(ARM64_PAGE_SHIFT_64K) & ~(SZ_2M - 1)) >> 12) > +alternative_endif > +.Lfinish_falkor_e1003\@: > isb > tlbi vae1, \tmp > dsb nsh > -alternative_else_nop_endif > +.Lskip_falkor_e1003\@: > #endif /* CONFIG_QCOM_FALKOR_ERRATUM_1003 */ > .endm > > -- > 2.43.0 >
