linux-kernel - Re: [PATCH 1/3] arm64: clean up trampoline vector loads

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Message-ID: <2067644.cOvikPKVsA@basile.remlab.net>
Date:   Mon, 23 Mar 2020 22:42:30 +0200
From:   Rémi Denis-Courmont <remi@...lab.net>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Mark Rutland <mark.rutland@....com>, will@...nel.org,
        james.morse@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] arm64: clean up trampoline vector loads

Le maanantaina 23. maaliskuuta 2020, 21.04.09 EET Catalin Marinas a écrit :
> On Mon, Mar 23, 2020 at 12:14:37PM +0000, Mark Rutland wrote:
> > On Mon, Mar 23, 2020 at 02:08:53PM +0200, Rémi Denis-Courmont wrote:
> > > Le maanantaina 23. maaliskuuta 2020, 14.07.00 EET Mark Rutland a écrit :
> > > > 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.
> > > 
> > > IMU, ADRP gives a 4K aligned value, regardless of MMU (TCR) settings.
> > 
> > Sorry, I had erroneously assumed tramp_vectors was page aligned. The
> > issue still stands -- we haven't accounted for bits 15:12, as those can
> > differ between tramp_vectors and __entry_tramp_data_start.

Does that mean that the SDEI code never worked with page size > 4 KiB?

> Should we just use adrp on __entry_tramp_data_start? Anyway, the diff
> below doesn't solve the issue I'm seeing (only reverting patch 3).

AFAIU, the preexisting code uses the manual PAGE_SIZE offset because the offset 
in the main vmlinux does not match the architected offset inside the fixmap. If 
so, then using the symbol directly will not work at all.




> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index ca1340eb46d8..4cc9d1df3985 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -810,7 +810,7 @@ alternative_else_nop_endif
>  2:
>  	tramp_map_kernel	x30
>  #ifdef CONFIG_RANDOMIZE_BASE
> -	adrp	x30, tramp_vectors + PAGE_SIZE
> +	adrp	x30, __entry_tramp_data_start
>  alternative_insn isb, nop, ARM64_WORKAROUND_QCOM_FALKOR_E1003
>  	ldr	x30, [x30, #:lo12:__entry_tramp_data_start]
>  #else
> @@ -964,7 +964,7 @@ SYM_CODE_START(__sdei_asm_entry_trampoline)
>  1:	str	x4, [x1, #(SDEI_EVENT_INTREGS + S_ORIG_ADDR_LIMIT)]
> 
>  #ifdef CONFIG_RANDOMIZE_BASE
> -	adrp	x4, tramp_vectors + PAGE_SIZE
> +	adrp	x4, __sdei_asm_trampoline_next_handler
>  	ldr	x4, [x4, #:lo12:__sdei_asm_trampoline_next_handler]
>  #else
>  	ldr	x4, =__sdei_asm_handler


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