Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753250AbbKMH7u (ORCPT ); Fri, 13 Nov 2015 02:59:50 -0500 Received: from mail.skyhub.de ([78.46.96.112]:34306 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750779AbbKMH7s (ORCPT ); Fri, 13 Nov 2015 02:59:48 -0500 Date: Fri, 13 Nov 2015 08:59:43 +0100 From: Borislav Petkov To: Matt Fleming Cc: Ingo Molnar , Thomas Gleixner , "H . Peter Anvin" , Toshi Kani , linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org, Sai Praneeth Prakhya , Linus Torvalds , Dave Jones , Andrew Morton , Andy Lutomirski , Denys Vlasenko , Stephen Smalley Subject: Re: [PATCH 4/6] x86/efi: Hoist page table switching code into efi_call_virt() Message-ID: <20151113075943.GB23605@pd.tnic> References: <1447342823-3612-1-git-send-email-matt@codeblueprint.co.uk> <1447342823-3612-5-git-send-email-matt@codeblueprint.co.uk> <20151112184432.GG3838@pd.tnic> <20151112200108.GF2681@codeblueprint.co.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20151112200108.GF2681@codeblueprint.co.uk> 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: 1690 Lines: 45 On Thu, Nov 12, 2015 at 08:01:08PM +0000, Matt Fleming wrote: > > That PUSHF implicitly pushes on the stack pointed by %rsp. But(!) we > > have switched the pagetable (i.e., %cr3 has efi_scratch.efi_pgt) and > > we're pushing to the VA where the stack *was* but is not anymore. > > All the kernel mappings will still exist in the page table we switch > to, so pushing to the stack should be fine. > > The mappings have to exist so that the firmware can dereference > pointer arguments, e.g. when writing variable data to a kernel buffer. > > Or have I misunderstood your point? > > > Or maybe it is because you're copying all the PUDs. It is still not 100% > > clean, IMHO. ^^^^^^^^^^^^^^^^^ I think we're on the same page - you're copying the PUDs in efi_sync_low_kernel_mappings() so the stack should be there. > > Can you do the prolog/epilog calls inside the IRQs-off section? > > Not really because in the efi_enabled(EFI_OLD_MEMMAP) case we perform > kmalloc(), see commit 23a0d4e8fa6d ("efi: Disable interrupts around > EFI calls, not in the epilog/prolog calls"). n_pgds = DIV_ROUND_UP((max_pfn << PAGE_SHIFT), PGDIR_SIZE); save_pgd = kmalloc(n_pgds * sizeof(pgd_t), GFP_KERNEL); This? That n_pgds thing is of static size so you can pre-alloc it maybe even once during boot and reuse it all the time when EFI_OLD_MEMMAP is enabled. -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/