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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8800AC43334 for ; Wed, 8 Jun 2022 08:01:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229680AbiFHIBs (ORCPT ); Wed, 8 Jun 2022 04:01:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49642 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230012AbiFHIBb (ORCPT ); Wed, 8 Jun 2022 04:01:31 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EEB1623B949 for ; Wed, 8 Jun 2022 00:34:10 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id B992E614FC for ; Wed, 8 Jun 2022 07:34:05 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 22DD2C34116; Wed, 8 Jun 2022 07:34:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1654673645; bh=zUAriSoqt7X75BSYiptDA8HT+jFpatA1VwWFOOuCHJU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=qEaE9E6N5v30L8JQ3VERoWqoGcxl8hjBVPm9K5ojoQJfgnnWatnqWxG4DP8/xS08Y owgC1hj6TgQHhVZmWYY07U4Hr4n7znTtDHnqs84R3TKN5D6JAaOti4R2JeDo4yPd86 LGx2N9NpwuDbOuk+nao/8IwB8iIyRqwtRG1NSmDkbd7OU9NHPkZV+kM/RMaGs7GksU o5Nvb/O3ljrUr4Y+aY6Z2Ub4n7QZPPuwSFhI+7WsT+gkooyreYBFNJwr9iysfWhfIw lIcr5/Utb29CLYN2QUa/09Zn+YLbk6pfaNGBlRvSY2C1yAReeyCxIEnhV1qnGHK51b pSCFuLuNYzfuQ== Received: from ip-185-104-136-29.ptr.icomera.net ([185.104.136.29] helo=wait-a-minute.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1nyqCY-00GWcs-UT; Wed, 08 Jun 2022 08:34:03 +0100 Date: Wed, 08 Jun 2022 08:33:59 +0100 Message-ID: <87k09rzk0o.wl-maz@kernel.org> From: Marc Zyngier To: Kalesh Singh Cc: mark.rutland@arm.com, broonie@kernel.org, will@kernel.org, qperret@google.com, tabba@google.com, surenb@google.com, tjmercier@google.com, kernel-team@android.com, James Morse , Alexandru Elisei , Suzuki K Poulose , Catalin Marinas , Masami Hiramatsu , Alexei Starovoitov , "Madhavan T. Venkataraman" , Peter Zijlstra , Andrew Jones , Zenghui Yu , Kefeng Wang , Keir Fraser , Ard Biesheuvel , Oliver Upton , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 3/5] KVM: arm64: Add hypervisor overflow stack In-Reply-To: <20220607165105.639716-4-kaleshsingh@google.com> References: <20220607165105.639716-1-kaleshsingh@google.com> <20220607165105.639716-4-kaleshsingh@google.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.104.136.29 X-SA-Exim-Rcpt-To: kaleshsingh@google.com, mark.rutland@arm.com, broonie@kernel.org, will@kernel.org, qperret@google.com, tabba@google.com, surenb@google.com, tjmercier@google.com, kernel-team@android.com, james.morse@arm.com, alexandru.elisei@arm.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, mhiramat@kernel.org, ast@kernel.org, madvenka@linux.microsoft.com, peterz@infradead.org, drjones@redhat.com, yuzenghui@huawei.com, wangkefeng.wang@huawei.com, keirf@google.com, ardb@kernel.org, oupton@google.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 07 Jun 2022 17:50:45 +0100, Kalesh Singh wrote: > > Allocate and switch to 16-byte aligned secondary stack on overflow. This > provides us stack space to better handle overflows; and is used in > a subsequent patch to dump the hypervisor stacktrace. > > Signed-off-by: Kalesh Singh > --- > arch/arm64/kernel/stacktrace.c | 3 +++ > arch/arm64/kvm/hyp/nvhe/host.S | 9 ++------- > 2 files changed, 5 insertions(+), 7 deletions(-) > > diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c > index a84e38d41d38..f346b4c66f1c 100644 > --- a/arch/arm64/kernel/stacktrace.c > +++ b/arch/arm64/kernel/stacktrace.c > @@ -242,4 +242,7 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry, > > unwind(task, &state, consume_entry, cookie); > } > +#else /* __KVM_NVHE_HYPERVISOR__ */ > +DEFINE_PER_CPU(unsigned long [PAGE_SIZE/sizeof(long)], overflow_stack) > + __aligned(16); Does this need to be a whole page? With 64kB pages, this is potentially a lot of memory for something that will hardly ever be used. The rest of the kernel limits this to 4kB, which seems more reasonable. There is no guard page anyway, so PAGE_SIZE doesn't provide any extra protection. > #endif /* !__KVM_NVHE_HYPERVISOR__ */ > diff --git a/arch/arm64/kvm/hyp/nvhe/host.S b/arch/arm64/kvm/hyp/nvhe/host.S > index ea6a397b64a6..4e3032a244e1 100644 > --- a/arch/arm64/kvm/hyp/nvhe/host.S > +++ b/arch/arm64/kvm/hyp/nvhe/host.S > @@ -177,13 +177,8 @@ SYM_FUNC_END(__host_hvc) > b hyp_panic > > .L__hyp_sp_overflow\@: > - /* > - * Reset SP to the top of the stack, to allow handling the hyp_panic. > - * This corrupts the stack but is ok, since we won't be attempting > - * any unwinding here. > - */ > - ldr_this_cpu x0, kvm_init_params + NVHE_INIT_STACK_HYP_VA, x1 > - mov sp, x0 > + /* Switch to the overflow stack */ > + adr_this_cpu sp, overflow_stack + PAGE_SIZE, x0 > > b hyp_panic_bad_stack > ASM_BUG() > -- > 2.36.1.255.ge46751e96f-goog > > Thanks, M. -- Without deviation from the norm, progress is not possible.