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From: Thomas Gleixner <tglx@linutronix.de>
To: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Dave Hansen <dave.hansen@intel.com>,
	pbonzini@redhat.com, rkrcmar@redhat.com, mingo@redhat.com,
	bp@alien8.de, hpa@zytor.com, dave.hansen@linux.intel.com,
	luto@kernel.org, peterz@infradead.org, kvm@vger.kernel.org,
	x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	konrad.wilk@oracle.com, jan.setjeeilers@oracle.com,
	liran.alon@oracle.com, jwadams@google.com, graf@amazon.de,
	rppt@linux.vnet.ibm.com
Subject: Re: [RFC v2 00/27] Kernel Address Space Isolation
Date: Fri, 12 Jul 2019 18:00:42 +0200 (CEST)
Message-ID: <alpine.DEB.2.21.1907121751430.1788@nanos.tec.linutronix.de> (raw)
In-Reply-To: <61d5851e-a8bf-e25c-e673-b71c8b83042c@oracle.com>

On Fri, 12 Jul 2019, Alexandre Chartre wrote:
> On 7/12/19 12:44 PM, Thomas Gleixner wrote:
> > That ASI thing is just PTI on steroids.
> > 
> > So why do we need two versions of the same thing? That's absolutely bonkers
> > and will just introduce subtle bugs and conflicting decisions all over the
> > place.
> > 
> > The need for ASI is very tightly coupled to the need for PTI and there is
> > absolutely no point in keeping them separate.
> > 
> > The only difference vs. interrupts and exceptions is that the PTI logic
> > cares whether they enter from user or from kernel space while ASI only
> > cares about the kernel entry.
> 
> I think that's precisely what makes ASI and PTI different and independent.
> PTI is just about switching between userland and kernel page-tables, while
> ASI is about switching page-table inside the kernel. You can have ASI without
> having PTI. You can also use ASI for kernel threads so for code that won't
> be triggered from userland and so which won't involve PTI.

It's still the same concept. And you can argue in circles it does not
justify yet another mapping setup with is a different copy of some other
mapping setup. Whether PTI is replaced by ASI or PTI is extended to handle
ASI does not matter at all. Having two similar concepts side by side is a
guarantee for disaster.

> > So why do you want ot treat that differently? There is absolutely zero
> > reason to do so. And there is no reason to create a pointlessly different
> > version of PTI which introduces yet another variant of a restricted page
> > table instead of just reusing and extending what's there already.
> > 
> 
> As I've tried to explain, to me PTI and ASI are different and independent.
> PTI manages switching between userland and kernel page-table, and ASI manages
> switching between kernel and a reduced-kernel page-table.

Again. It's the same concept and it does not matter what form of reduced
page tables you use. You always need transition points and in order to make
the transition points work you need reliably mapped bits and pieces.

Also Paul wants to use the same concept for user space so trivial system
calls can do w/o PTI. In some other thread you said yourself that this
could be extended to cover the kvm ioctl, which is clearly a return to user
space.

Are we then going to add another set of randomly sprinkled transition
points and yet another 'state machine' to duct-tape the fallout?

Definitely not going to happen.

Thanks,

	tglx


  parent reply index

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-11 14:25 Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 01/26] mm/x86: Introduce kernel address space isolation Alexandre Chartre
2019-07-11 21:33   ` Thomas Gleixner
2019-07-12  7:43     ` Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 02/26] mm/asi: Abort isolation on interrupt, exception and context switch Alexandre Chartre
2019-07-11 20:11   ` Andi Kleen
2019-07-11 20:17     ` Mike Rapoport
2019-07-11 20:41       ` Alexandre Chartre
2019-07-12  0:05   ` Andy Lutomirski
2019-07-12  7:50     ` Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 03/26] mm/asi: Handle page fault due to address space isolation Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 04/26] mm/asi: Functions to track buffers allocated for an ASI page-table Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 05/26] mm/asi: Add ASI page-table entry offset functions Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 06/26] mm/asi: Add ASI page-table entry allocation functions Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 07/26] mm/asi: Add ASI page-table entry set functions Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 08/26] mm/asi: Functions to populate an ASI page-table from a VA range Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 09/26] mm/asi: Helper functions to map module into ASI Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 10/26] mm/asi: Keep track of VA ranges mapped in ASI page-table Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 11/26] mm/asi: Functions to clear ASI page-table entries for a VA range Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 12/26] mm/asi: Function to copy page-table entries for percpu buffer Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 13/26] mm/asi: Add asi_remap() function Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 14/26] mm/asi: Handle ASI mapped range leaks and overlaps Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 15/26] mm/asi: Initialize the ASI page-table with core mappings Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 16/26] mm/asi: Option to map current task into ASI Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 17/26] rcu: Move tree.h static forward declarations to tree.c Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 18/26] rcu: Make percpu rcu_data non-static Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 19/26] mm/asi: Add option to map RCU data Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 20/26] mm/asi: Add option to map cpu_hw_events Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 21/26] mm/asi: Make functions to read cr3/cr4 ASI aware Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 22/26] KVM: x86/asi: Introduce address_space_isolation module parameter Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 23/26] KVM: x86/asi: Introduce KVM address space isolation Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 24/26] KVM: x86/asi: Populate the KVM ASI page-table Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 25/26] KVM: x86/asi: Switch to KVM address space on entry to guest Alexandre Chartre
2019-07-11 14:25 ` [RFC v2 26/26] KVM: x86/asi: Map KVM memslots and IO buses into KVM ASI Alexandre Chartre
2019-07-11 14:40 ` [RFC v2 00/27] Kernel Address Space Isolation Alexandre Chartre
2019-07-11 22:38 ` Dave Hansen
2019-07-12  8:09   ` Alexandre Chartre
2019-07-12 13:51     ` Dave Hansen
2019-07-12 14:06       ` Alexandre Chartre
2019-07-12 15:23         ` Thomas Gleixner
2019-07-12 10:44   ` Thomas Gleixner
2019-07-12 11:56     ` Alexandre Chartre
2019-07-12 12:50       ` Peter Zijlstra
2019-07-12 13:43         ` Alexandre Chartre
2019-07-12 13:58           ` Dave Hansen
2019-07-12 14:36           ` Andy Lutomirski
2019-07-14 18:17             ` Alexander Graf
2019-07-12 13:54         ` Dave Hansen
2019-07-12 15:20           ` Peter Zijlstra
2019-07-12 15:16         ` Thomas Gleixner
2019-07-12 16:37           ` Alexandre Chartre
2019-07-12 16:45             ` Andy Lutomirski
2019-07-14 17:11               ` Mike Rapoport
2019-07-12 19:06             ` Peter Zijlstra
2019-07-14 15:06               ` Andy Lutomirski
2019-07-15 10:33                 ` Peter Zijlstra
2019-07-12 19:48             ` Thomas Gleixner
2019-07-15  8:23               ` Alexandre Chartre
2019-07-15  8:28                 ` Thomas Gleixner
2019-07-12 16:00       ` Thomas Gleixner [this message]
2019-07-12 11:44 ` Peter Zijlstra
2019-07-12 12:17   ` Alexandre Chartre
2019-07-12 12:36     ` Peter Zijlstra
2019-07-12 12:47       ` Alexandre Chartre
2019-07-12 13:07         ` Peter Zijlstra
2019-07-12 13:46           ` Alexandre Chartre
2019-07-31 16:31             ` Dario Faggioli
2019-08-22 12:31               ` Alexandre Chartre

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