From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 76BBEC43460 for ; Wed, 14 Apr 2021 09:00:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5CE7361158 for ; Wed, 14 Apr 2021 09:00:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350395AbhDNJBH (ORCPT ); Wed, 14 Apr 2021 05:01:07 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:38979 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350259AbhDNJAN (ORCPT ); Wed, 14 Apr 2021 05:00:13 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618390777; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=+7RKdsYE9Dit9s7fqKe4htpbMtGwJmEzBNvN06lrEuM=; b=hpcRFkV6DNU5wnEx8H9QsM/UmRrYp1IJJHYWp6SsUmMda2NrTOhbdcS/D/IoritO1RDgX3 frDSN1vI7craSTy9Rc/7nJALPxn/A/UWoV2Wgzz6FUVdGcAohapQugN9/ba2dIBG2Z2BiE cjRDeiydlbdq0WVvc8HRTQKb+yIeqd0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-1-WpdarJk9PDiDQU8sr6jrMA-1; Wed, 14 Apr 2021 04:59:35 -0400 X-MC-Unique: WpdarJk9PDiDQU8sr6jrMA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 772778030A0; Wed, 14 Apr 2021 08:59:34 +0000 (UTC) Received: from kamzik.brq.redhat.com (unknown [10.40.192.57]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 33A7362499; Wed, 14 Apr 2021 08:59:24 +0000 (UTC) Date: Wed, 14 Apr 2021 10:59:21 +0200 From: Andrew Jones To: Alexandru Elisei Cc: kvm@vger.kernel.org, nikos.nikoleris@arm.com, andre.przywara@arm.com, eric.auger@redhat.com Subject: Re: [PATCH kvm-unit-tests 1/8] arm/arm64: Reorganize cstart assembler Message-ID: <20210414085921.lazllz24o3eqts52@kamzik.brq.redhat.com> References: <20210407185918.371983-1-drjones@redhat.com> <20210407185918.371983-2-drjones@redhat.com> <2b647637-d307-5256-beab-c58728f60e9b@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2b647637-d307-5256-beab-c58728f60e9b@arm.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, Apr 13, 2021 at 05:34:24PM +0100, Alexandru Elisei wrote: > Hi Drew, > > On 4/7/21 7:59 PM, Andrew Jones wrote: > > Move secondary_entry helper functions out of .init and into .text, > > since secondary_entry isn't run at "init" time. > > The tests aren't loaded using the loader, so as far as I can tell the reason for > having an .init section is to make sure the code from the start label is put at > offset 0 in the test binary. As long as the start label is kept at the beginning > of the .init section, and the loader script places the section first, I don't see > any issues with this change. > > The only hypothetical problem that I can think of is that the code from .init > calls code from .text, and if the text section grows very large we might end up > with a PC offset larger than what can be encoded in the BL instruction. That's > unlikely to happen (the offset is 16MB for arm and 64MB for arm64), and the .init > code already calls other functions (like setup) which are in .text, so we would > have this problem regardless of this change. And the compiler will emit an error > if that happens. > > > > > Signed-off-by: Andrew Jones > > --- > > arm/cstart.S | 62 +++++++++++++++++++++++++++----------------------- > > arm/cstart64.S | 22 +++++++++++------- > > 2 files changed, 48 insertions(+), 36 deletions(-) > > > > diff --git a/arm/cstart.S b/arm/cstart.S > > index d88a98362940..653ab1e8a141 100644 > > --- a/arm/cstart.S > > +++ b/arm/cstart.S > > @@ -96,32 +96,7 @@ start: > > bl exit > > b halt > > > > - > > -.macro set_mode_stack mode, stack > > - add \stack, #S_FRAME_SIZE > > - msr cpsr_c, #(\mode | PSR_I_BIT | PSR_F_BIT) > > - isb > > - mov sp, \stack > > -.endm > > - > > -exceptions_init: > > - mrc p15, 0, r2, c1, c0, 0 @ read SCTLR > > - bic r2, #CR_V @ SCTLR.V := 0 > > - mcr p15, 0, r2, c1, c0, 0 @ write SCTLR > > - ldr r2, =vector_table > > - mcr p15, 0, r2, c12, c0, 0 @ write VBAR > > - > > - mrs r2, cpsr > > - > > - /* first frame reserved for svc mode */ > > - set_mode_stack UND_MODE, r0 > > - set_mode_stack ABT_MODE, r0 > > - set_mode_stack IRQ_MODE, r0 > > - set_mode_stack FIQ_MODE, r0 > > - > > - msr cpsr_cxsf, r2 @ back to svc mode > > - isb > > - mov pc, lr > > +.text > > Hm... now we've moved enable_vfp from .init to .text, and enable_vfp *is* called > from .init code, which doesn't fully match up with the commit message. Is the > actual reason for this change that the linker script for EFI will discard the > .init section? Maybe it's worth mentioning that in the commit message, because it > will explain this change better. Right, the .init section may not exist when linking with other linker scripts. I'll make the commit message more clear. > Or is it to align arm with arm64, where only > start is in the .init section? > > > > > enable_vfp: > > /* Enable full access to CP10 and CP11: */ > > @@ -133,8 +108,6 @@ enable_vfp: > > vmsr fpexc, r0 > > mov pc, lr > > > > -.text > > - > > .global get_mmu_off > > get_mmu_off: > > ldr r0, =auxinfo > > @@ -235,6 +208,39 @@ asm_mmu_disable: > > > > mov pc, lr > > > > +/* > > + * Vectors > > + */ > > + > > +.macro set_mode_stack mode, stack > > + add \stack, #S_FRAME_SIZE > > + msr cpsr_c, #(\mode | PSR_I_BIT | PSR_F_BIT) > > + isb > > + mov sp, \stack > > +.endm > > + > > +exceptions_init: > > + mrc p15, 0, r2, c1, c0, 0 @ read SCTLR > > + bic r2, #CR_V @ SCTLR.V := 0 > > + mcr p15, 0, r2, c1, c0, 0 @ write SCTLR > > + ldr r2, =vector_table > > + mcr p15, 0, r2, c12, c0, 0 @ write VBAR > > + > > + mrs r2, cpsr > > + > > + /* > > + * Input r0 is the stack top, which is the exception stacks base > > + * The first frame is reserved for svc mode > > + */ > > + set_mode_stack UND_MODE, r0 > > + set_mode_stack ABT_MODE, r0 > > + set_mode_stack IRQ_MODE, r0 > > + set_mode_stack FIQ_MODE, r0 > > + > > + msr cpsr_cxsf, r2 @ back to svc mode > > + isb > > + mov pc, lr > > + > > /* > > * Vector stubs > > * Simplified version of the Linux kernel implementation > > diff --git a/arm/cstart64.S b/arm/cstart64.S > > index 0a85338bcdae..d39cf4dfb99c 100644 > > --- a/arm/cstart64.S > > +++ b/arm/cstart64.S > > @@ -89,10 +89,12 @@ start: > > msr cpacr_el1, x4 > > > > /* set up exception handling */ > > + mov x4, x0 // x0 is the addr of the dtb > > I suppose changing exceptions_init to use x0 as a scratch register instead of x4 > makes some sense if you look at it from the perspective of it being called from > secondary_entry, where all the functions use x0 as a scratch register. But it's > still called from start, where using x4 as a scratch register is preferred because > of the kernel boot protocol (x0-x3 are reserved). > > Is there an actual bug that this is supposed to fix (I looked for it and couldn't > figure it out) or is it just a cosmetic change? Now that exceptions_init isn't a private function of start (actually it hasn't been in a long time, considering secondary_entry calls it) I would like it to better conform to calling conventions. I guess I should have used x19 here instead of x4 to be 100% correct. Or, would you rather I just continue using x4 in exceptions_init in order to avoid the save/restore? Thanks, drew