From mboxrd@z Thu Jan 1 00:00:00 1970 From: Martin Schwidefsky Subject: Re: [PATCH RFC 0/2] KVM: s390: avoid having to enable vm.alloc_pgste Date: Thu, 8 Jun 2017 13:24:01 +0200 Message-ID: <20170608132401.5eafacc4@mschwideX1> References: <20170529163202.13077-1-david@redhat.com> <20170601124651.3e7969ab@mschwideX1> <20170602070210.GA4221@osiris> <20170602114647.35e6d30f@mschwideX1> <2d45c9d5-2108-7408-e7cd-44b9f6d03b0f@de.ibm.com> <20170602125345.5ac9e12e@mschwideX1> <63b5c762-fbbb-b6dc-0f2d-6837dac5bb04@de.ibm.com> <20170607143440.7c86af85@mschwideX1> <20170607204756.GA3143@osiris> <20170608073528.52b17428@mschwideX1> <20170608062531.GA3266@osiris> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Christian Borntraeger , David Hildenbrand , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Thomas Huth , Andreas Krebbel To: Heiko Carstens Return-path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:37412 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750914AbdFHLYV (ORCPT ); Thu, 8 Jun 2017 07:24:21 -0400 Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v58BOGjA141939 for ; Thu, 8 Jun 2017 07:24:21 -0400 Received: from e06smtp10.uk.ibm.com (e06smtp10.uk.ibm.com [195.75.94.106]) by mx0a-001b2d01.pphosted.com with ESMTP id 2axt7ybxam-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Thu, 08 Jun 2017 07:24:20 -0400 Received: from localhost by e06smtp10.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 8 Jun 2017 12:24:05 +0100 In-Reply-To: <20170608062531.GA3266@osiris> Sender: kvm-owner@vger.kernel.org List-ID: On Thu, 8 Jun 2017 08:25:31 +0200 Heiko Carstens wrote: > On Thu, Jun 08, 2017 at 07:35:28AM +0200, Martin Schwidefsky wrote: > > On Wed, 7 Jun 2017 22:47:56 +0200 > > Heiko Carstens wrote: > > > On Wed, Jun 07, 2017 at 02:34:40PM +0200, Martin Schwidefsky wrote: > > > > +#define arch_elf_pt_proc(ehdr, phdr, elf, interp, state) \ > > > > +({ \ > > > > + struct elf64_hdr *_ehdr = (void *) ehdr; \ > > > > + struct elf64_phdr *_phdr = (void *) phdr; \ > > > > + int _rc = 0; \ > > > > + if (_ehdr->e_ident[EI_CLASS] == ELFCLASS64 && \ > > > > + _phdr->p_type == PT_S390_REQUEST_PGSTE && \ > > > > + !page_table_allocate_pgste && \ > > > > + !test_thread_flag(TIF_REQUEST_PGSTE)) { \ > > > > + set_thread_flag(TIF_REQUEST_PGSTE); \ > > > > + set_pt_regs_flag(task_pt_regs(current), \ > > > > + PIF_SYSCALL_RESTART); \ > > > > + _rc = -EAGAIN; \ > > > > + } \ > > > > + _rc; \ > > > > +}) > > > > > > I'm wondering if this should simply fail, if a PT_S390_REQUEST_PGSTE type > > > segment exists, but it is not ELFCLASS64? > > > It will fail later anyway on s390_enable_sie(), but... > > > > Does it matter if it fails for a 32-bit ELF file? Just makes the code more > > complex without benefit, no? > > It would be more consistent, since right now a 32-bit ELF file with > PT_S390_REQUEST_PGSTE will be exectuted, but the page tables won't have any > pgstes. That's sort of odd, isn't it? And that later on it won't be able to > create a virtual machine because our current implementation doesn't allow > that for compat tasks is sort of unrelated. > But anyway, I'll leave that up to you, it doesn't really matter. Actually the code will be less complex if we add PT_S390_REQUEST_PGSTE for 32-bit ELF files as well. It does not make sense to define the segment for a compat process as KVM won't work but you get what you ask for.. This looks like this: #define arch_elf_pt_proc(ehdr, phdr, elf, interp, state) \ ({ \ int _rc = 0; \ if (phdr->p_type == PT_S390_REQUEST_PGSTE && \ !page_table_allocate_pgste && \ !test_thread_flag(TIF_REQUEST_PGSTE)) { \ set_thread_flag(TIF_REQUEST_PGSTE); \ set_pt_regs_flag(task_pt_regs(current), \ PIF_SYSCALL_RESTART); \ _rc = -EAGAIN; \ } \ _rc; \ }) phdr is a (struct elf_phd *) which is either define to a a (struct elf64_phdr *) or a (struct elf32_phdr *). The check works in both cases. > > > > > > diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h > > > > index c119d564d8f2..1201b18e817d 100644 > > > > --- a/arch/s390/include/asm/mmu_context.h > > > > +++ b/arch/s390/include/asm/mmu_context.h > > > > @@ -25,7 +25,8 @@ static inline int init_new_context(struct task_struct *tsk, > > > > mm->context.gmap_asce = 0; > > > > mm->context.flush_mm = 0; > > > > #ifdef CONFIG_PGSTE > > > > - mm->context.alloc_pgste = page_table_allocate_pgste; > > > > + mm->context.alloc_pgste = page_table_allocate_pgste || > > > > + test_thread_flag(TIF_REQUEST_PGSTE); > > > > > > I think the alloc_pgste flag should be inherited on fork, no? > > > > Yes, that makes it more consistent. I'll add it. > > By the way, what prevents with the _current_ code a scenario like: > > - set allocate_pgste sysctl to 1 > - create kvm guest > - s390_enable_sie > - run vcpu > - set allocate_pgste sysctl to 0 > - clone(... CLONE_FILES ...) (that is: new mm without pgstes, but shared fds) > - [child] run vcpu > > Is there anything that makes sure we cannot execute the sie instruction in > the child process? Yes, that looks like a loop-hole. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin.