Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752548AbdI0JNW (ORCPT ); Wed, 27 Sep 2017 05:13:22 -0400 Received: from foss.arm.com ([217.140.101.70]:42978 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752331AbdI0JNT (ORCPT ); Wed, 27 Sep 2017 05:13:19 -0400 Date: Wed, 27 Sep 2017 10:13:33 +0100 From: Will Deacon To: Marc Zyngier Cc: Yury Norov , Catalin Marinas , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org Subject: Re: [PATCH] arm64: fix documentation on kernel pages mappings to HYP VA Message-ID: <20170927091332.GA19317@arm.com> References: <20170913180830.8608-1-ynorov@caviumnetworks.com> <20170926184542.t56zpdx2s5et77gy@yury-thinkpad> <86bmlwo842.fsf@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <86bmlwo842.fsf@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4351 Lines: 97 On Wed, Sep 27, 2017 at 09:31:41AM +0100, Marc Zyngier wrote: > On Tue, Sep 26 2017 at 9:45:42 pm BST, Yury Norov wrote: > > On Wed, Sep 13, 2017 at 09:08:30PM +0300, Yury Norov wrote: > >> The Documentation/arm64/memory.txt says: > >> When using KVM, the hypervisor maps kernel pages in EL2, at a fixed > >> offset from the kernel VA (top 24bits of the kernel VA set to zero): > >> > >> In fact, kernel addresses are transleted to HYP with kern_hyp_va macro, > >> which has more options, and none of them assumes clearing of top 24bits > >> of the kernel VA. > >> > >> Signed-off-by: Yury Norov > >> --- > >> Documentation/arm64/memory.txt | 15 +++++++++------ > >> 1 file changed, 9 insertions(+), 6 deletions(-) > >> > >> diff --git a/Documentation/arm64/memory.txt b/Documentation/arm64/memory.txt > >> index d7273a5f6456..c39895d7e3a2 100644 > >> --- a/Documentation/arm64/memory.txt > >> +++ b/Documentation/arm64/memory.txt > >> @@ -86,9 +86,12 @@ Translation table lookup with 64KB pages: > >> +-------------------------------------------------> [63] TTBR0/1 > >> > >> > >> -When using KVM, the hypervisor maps kernel pages in EL2, at a fixed > >> -offset from the kernel VA (top 24bits of the kernel VA set to zero): > >> - > >> -Start End Size Use > >> ------------------------------------------------------------------------ > >> -0000004000000000 0000007fffffffff 256GB kernel objects mapped in HYP > >> +When using KVM without Virtualization Host Extensions, the hypervisor maps > >> +kernel pages in EL2, at a fixed offset from the kernel VA. Namely, top 16 > >> +or 25 bits of the kernel VA set to zero depending on ARM64_VA_BITS_48 or > >> +ARM64_VA_BITS_39 config option selected; or top 17 or 26 bits of the kernel > >> +VA set to zero if CPU has Reduced HYP mapping offset capability. See > >> +kern_hyp_va macro. > > What is this "Reduced HYP mapping offset capability"? > > You're missing the point that the location of the EL2 mapping is > conditioned by the location of the identity mapping that is used to > bring up / tear down KVM. You have to express the VA transformation in > terms of both VA_BITS (and there is more cases than just 39 or 48 bits) > *and* the idmap address, not to mention the case where KVM's VA_BITS is > larger than the rest of the kernel. See the extensive blurb in > kvm_mmu.h. > > >> + > >> +When using KVM with Virtualization Host Extensions, no additional mappings > >> +created as host kernel already operates in EL2. > > This bit is fine. FWIW, I was going to queue a simplified version along the lines of the patch below. Will --->8 commit dbf7393b7738a0ba0284551e7b6e014cfb100661 Author: Yury Norov Date: Wed Sep 13 21:08:30 2017 +0300 arm64: fix documentation on kernel pages mappings to HYP VA The Documentation/arm64/memory.txt says: When using KVM, the hypervisor maps kernel pages in EL2, at a fixed offset from the kernel VA (top 24bits of the kernel VA set to zero): In fact, kernel addresses are transleted to HYP with kern_hyp_va macro, which has more options, and none of them assumes clearing of top 24bits of the kernel VA. Signed-off-by: Yury Norov [will: removed gory details] Signed-off-by: Will Deacon diff --git a/Documentation/arm64/memory.txt b/Documentation/arm64/memory.txt index d7273a5f6456..ea9ee39784a2 100644 --- a/Documentation/arm64/memory.txt +++ b/Documentation/arm64/memory.txt @@ -86,9 +86,9 @@ Translation table lookup with 64KB pages: +-------------------------------------------------> [63] TTBR0/1 -When using KVM, the hypervisor maps kernel pages in EL2, at a fixed -offset from the kernel VA (top 24bits of the kernel VA set to zero): +When using KVM without the Virtualization Host Extensions, the hypervisor +maps kernel pages in EL2 at a fixed offset from the kernel VA. See the +kern_hyp_va macro for more details. -Start End Size Use ------------------------------------------------------------------------ -0000004000000000 0000007fffffffff 256GB kernel objects mapped in HYP +When using KVM with the Virtualization Host Extensions, no additional +mappings are created, since the host kernel runs directly in EL2.