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Date: Mon, 23 Mar 2020 12:07:00 +0000 From: Mark Rutland <mark.rutland@....com> To: Rémi Denis-Courmont <remi@...lab.net> Cc: catalin.marinas@....com, will@...nel.org, linux-arm-kernel@...ts.infradead.org, james.morse@....com, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/3] arm64: clean up trampoline vector loads On Thu, Mar 19, 2020 at 11:14:05AM +0200, Rémi Denis-Courmont wrote: > From: Rémi Denis-Courmont <remi.denis.courmont@...wei.com> > > This switches from custom instruction patterns to the regular large > memory model sequence with ADRP and LDR. In doing so, the ADD > instruction can be eliminated in the SDEI handler, and the code no > longer assumes that the trampoline vectors and the vectors address both > start on a page boundary. > > Signed-off-by: Rémi Denis-Courmont <remi.denis.courmont@...wei.com> > --- > arch/arm64/kernel/entry.S | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index e5d4e30ee242..24f828739696 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -805,9 +805,9 @@ alternative_else_nop_endif > 2: > tramp_map_kernel x30 > #ifdef CONFIG_RANDOMIZE_BASE > - adr x30, tramp_vectors + PAGE_SIZE > + adrp x30, tramp_vectors + PAGE_SIZE > alternative_insn isb, nop, ARM64_WORKAROUND_QCOM_FALKOR_E1003 > - ldr x30, [x30] > + ldr x30, [x30, #:lo12:__entry_tramp_data_start] I think this is busted for !4K kernels once we reduce the alignment of __entry_tramp_data_start. The ADRP gives us a 64K aligned address (with bits 15:0 clear). The lo12 relocation gives us bits 11:0, so we haven't accounted for bits 15:12. I think that's what's causing the hang Catalin sees with 64K pages (and would also be a problem for 16K pages). Ideally, we'd account for those bits with the ADRP, but I'm not sure that an ELF relocation can encode symbol + addr + symbol:15-12, so we likely nned more instructions to explicitly mask that in. ... either that, or leave this page aligned. > #else > ldr x30, =vectors > #endif > @@ -953,9 +953,8 @@ SYM_CODE_START(__sdei_asm_entry_trampoline) > 1: str x4, [x1, #(SDEI_EVENT_INTREGS + S_ORIG_ADDR_LIMIT)] > > #ifdef CONFIG_RANDOMIZE_BASE > - adr x4, tramp_vectors + PAGE_SIZE > - add x4, x4, #:lo12:__sdei_asm_trampoline_next_handler > - ldr x4, [x4] > + adrp x4, tramp_vectors + PAGE_SIZE > + ldr x4, [x4, #:lo12:__sdei_asm_trampoline_next_handler] Likewise here. Thanks, Mark. > #else > ldr x4, =__sdei_asm_handler > #endif > -- > 2.26.0.rc2 >
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