Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966181AbbKFDjR (ORCPT ); Thu, 5 Nov 2015 22:39:17 -0500 Received: from userp1040.oracle.com ([156.151.31.81]:17650 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965917AbbKFDip (ORCPT ); Thu, 5 Nov 2015 22:38:45 -0500 Subject: Re: [PATCH] x86/mm: Skip the hypervisor range when walking PGD To: "H. Peter Anvin" , tglx@linutronix.de, mingo@redhat.com References: <1446749795-27764-1-git-send-email-boris.ostrovsky@oracle.com> <563BD8D6.107@zytor.com> Cc: x86@kernel.org, linux-kernel@vger.kernel.org, linux@eikelenboom.it, xen-devel@lists.xen.org From: Boris Ostrovsky Message-ID: <563C20AC.5020308@oracle.com> Date: Thu, 5 Nov 2015 22:38:20 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <563BD8D6.107@zytor.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: userv0022.oracle.com [156.151.31.74] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2799 Lines: 69 On 11/05/2015 05:31 PM, H. Peter Anvin wrote: > On 11/05/15 10:56, Boris Ostrovsky wrote: >> The range between 0xffff800000000000 and 0xffff87ffffffffff is reserved >> for hypervisor and therefore we should not try to follow PGD's indexes >> corresponding to those addresses. >> >> While this has alsways been a problem, with commit e1a58320a38d ("x86/mm: >> Warn on W^X mappings") ptdump_walk_pgd_level_core() can now be called >> during boot, causing a PV Xen guest to crash. >> >> Reported-by: Sander Eikelenboom >> Signed-off-by: Boris Ostrovsky >> --- >> arch/x86/mm/dump_pagetables.c | 7 ++++++- >> 1 file changed, 6 insertions(+), 1 deletion(-) >> >> diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c >> index 1bf417e..756c921 100644 >> --- a/arch/x86/mm/dump_pagetables.c >> +++ b/arch/x86/mm/dump_pagetables.c >> @@ -362,8 +362,13 @@ static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd, >> bool checkwx) >> { >> #ifdef CONFIG_X86_64 >> +/* ffff800000000000 - ffff87ffffffffff is reserved for hypervisor */ >> +#define is_hypervisor_range(idx) (paravirt_enabled() && \ >> + (((idx) >= pgd_index(__PAGE_OFFSET) - 16) && \ >> + ((idx) < pgd_index(__PAGE_OFFSET)))) >> pgd_t *start = (pgd_t *) &init_level4_pgt; >> #else >> +#define is_hypervisor_range(idx) 0 >> pgd_t *start = swapper_pg_dir; >> #endif >> pgprotval_t prot; >> @@ -381,7 +386,7 @@ static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd, >> >> for (i = 0; i < PTRS_PER_PGD; i++) { >> st.current_address = normalize_addr(i * PGD_LEVEL_MULT); >> - if (!pgd_none(*start)) { >> + if (!pgd_none(*start) && !is_hypervisor_range(i)) { >> if (pgd_large(*start) || !pgd_present(*start)) { >> prot = pgd_flags(*start); >> note_page(m, &st, __pgprot(prot), 1); >> > Maybe we could use the max_lines field in the address_markers[] array? > We really shouldn't be mapping anything in the hypervisor space even on > native. You mean overload max_lines with a value indicating that the range needs to be skipped? That would require checking the range on each loop iteration since we update st.marker *after* we've walked a particular index. (And I think it would need to be done on each level to be generic). I could just drop paravirt_enabled() in is_hypervisor_range() but you are thinking about avoiding the macro altogether, right? (I do need to add hypervisor range to address_markers[]) -boris -- 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/