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Date: Tue, 13 Apr 2021 13:21:58 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Stephen Rothwell <sfr@...b.auug.org.au>
Cc: Christoffer Dall <cdall@...columbia.edu>,
Marc Zyngier <maz@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux Next Mailing List <linux-next@...r.kernel.org>,
Quentin Perret <qperret@...gle.com>
Subject: Re: linux-next: manual merge of the kvm-arm tree with the arm64 tree
On Tue, 13 Apr 2021 at 07:43, Stephen Rothwell <sfr@...b.auug.org.au> wrote:
>
> Hi all,
>
> Today's linux-next merge of the kvm-arm tree got a conflict in:
>
> arch/arm64/include/asm/assembler.h
>
> between commits:
>
> 27248fe1abb2 ("arm64: assembler: remove conditional NEON yield macros")
> 13150149aa6d ("arm64: fpsimd: run kernel mode NEON with softirqs disabled")
>
> from the arm64 tree
Those patches are on a topic branch 'for-next/neon-softirqs-disabled'
in the arm64 tree, so probably best to just pull that into kvm-arm and
fix the conflicts there.
> and commits:
>
> 8f4de66e247b ("arm64: asm: Provide set_sctlr_el2 macro")
> 755db23420a1 ("KVM: arm64: Generate final CTR_EL0 value when running in Protected mode")
>
> from the kvm-arm tree.
>
> I fixed it up (see below) and can carry the fix as necessary. This
> is now fixed as far as linux-next is concerned, but any non trivial
> conflicts should be mentioned to your upstream maintainer when your tree
> is submitted for merging. You may also want to consider cooperating
> with the maintainer of the conflicting tree to minimise any particularly
> complex conflicts.
>
> --
> Cheers,
> Stephen Rothwell
>
> diff --cc arch/arm64/include/asm/assembler.h
> index ab569b0b45fc,34ddd8a0f3dd..000000000000
> --- a/arch/arm64/include/asm/assembler.h
> +++ b/arch/arm64/include/asm/assembler.h
> @@@ -15,7 -15,7 +15,8 @@@
> #include <asm-generic/export.h>
>
> #include <asm/asm-offsets.h>
> +#include <asm/alternative.h>
> + #include <asm/asm-bug.h>
> #include <asm/cpufeature.h>
> #include <asm/cputype.h>
> #include <asm/debug-monitors.h>
> @@@ -701,25 -705,95 +714,33 @@@ USER(\label, ic ivau, \tmp2) // inval
> isb
> .endm
>
> + .macro set_sctlr_el1, reg
> + set_sctlr sctlr_el1, \reg
> + .endm
> +
> + .macro set_sctlr_el2, reg
> + set_sctlr sctlr_el2, \reg
> + .endm
> +
> -/*
> - * Check whether to yield to another runnable task from kernel mode NEON code
> - * (which runs with preemption disabled).
> - *
> - * if_will_cond_yield_neon
> - * // pre-yield patchup code
> - * do_cond_yield_neon
> - * // post-yield patchup code
> - * endif_yield_neon <label>
> - *
> - * where <label> is optional, and marks the point where execution will resume
> - * after a yield has been performed. If omitted, execution resumes right after
> - * the endif_yield_neon invocation. Note that the entire sequence, including
> - * the provided patchup code, will be omitted from the image if
> - * CONFIG_PREEMPTION is not defined.
> - *
> - * As a convenience, in the case where no patchup code is required, the above
> - * sequence may be abbreviated to
> - *
> - * cond_yield_neon <label>
> - *
> - * Note that the patchup code does not support assembler directives that change
> - * the output section, any use of such directives is undefined.
> - *
> - * The yield itself consists of the following:
> - * - Check whether the preempt count is exactly 1 and a reschedule is also
> - * needed. If so, calling of preempt_enable() in kernel_neon_end() will
> - * trigger a reschedule. If it is not the case, yielding is pointless.
> - * - Disable and re-enable kernel mode NEON, and branch to the yield fixup
> - * code.
> - *
> - * This macro sequence may clobber all CPU state that is not guaranteed by the
> - * AAPCS to be preserved across an ordinary function call.
> - */
> -
> - .macro cond_yield_neon, lbl
> - if_will_cond_yield_neon
> - do_cond_yield_neon
> - endif_yield_neon \lbl
> - .endm
> -
> - .macro if_will_cond_yield_neon
> -#ifdef CONFIG_PREEMPTION
> - get_current_task x0
> - ldr x0, [x0, #TSK_TI_PREEMPT]
> - sub x0, x0, #PREEMPT_DISABLE_OFFSET
> - cbz x0, .Lyield_\@
> - /* fall through to endif_yield_neon */
> - .subsection 1
> -.Lyield_\@ :
> -#else
> - .section ".discard.cond_yield_neon", "ax"
> -#endif
> - .endm
> -
> - .macro do_cond_yield_neon
> - bl kernel_neon_end
> - bl kernel_neon_begin
> - .endm
> -
> - .macro endif_yield_neon, lbl
> - .ifnb \lbl
> - b \lbl
> - .else
> - b .Lyield_out_\@
> - .endif
> - .previous
> -.Lyield_out_\@ :
> - .endm
> -
> /*
> - * Check whether preempt-disabled code should yield as soon as it
> - * is able. This is the case if re-enabling preemption a single
> - * time results in a preempt count of zero, and the TIF_NEED_RESCHED
> - * flag is set. (Note that the latter is stored negated in the
> - * top word of the thread_info::preempt_count field)
> + * Check whether preempt/bh-disabled asm code should yield as soon as
> + * it is able. This is the case if we are currently running in task
> + * context, and either a softirq is pending, or the TIF_NEED_RESCHED
> + * flag is set and re-enabling preemption a single time would result in
> + * a preempt count of zero. (Note that the TIF_NEED_RESCHED flag is
> + * stored negated in the top word of the thread_info::preempt_count
> + * field)
> */
> - .macro cond_yield, lbl:req, tmp:req
> -#ifdef CONFIG_PREEMPTION
> + .macro cond_yield, lbl:req, tmp:req, tmp2:req
> get_current_task \tmp
> ldr \tmp, [\tmp, #TSK_TI_PREEMPT]
> + /*
> + * If we are serving a softirq, there is no point in yielding: the
> + * softirq will not be preempted no matter what we do, so we should
> + * run to completion as quickly as we can.
> + */
> + tbnz \tmp, #SOFTIRQ_SHIFT, .Lnoyield_\@
> +#ifdef CONFIG_PREEMPTION
> sub \tmp, \tmp, #PREEMPT_DISABLE_OFFSET
> cbz \tmp, \lbl
> #endif
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