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From: Alexandre Chartre <alexandre.chartre@oracle.com>
To: Dave Hansen <dave.hansen@intel.com>,
	pbonzini@redhat.com, rkrcmar@redhat.com, tglx@linutronix.de,
	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
Cc: konrad.wilk@oracle.com, jan.setjeeilers@oracle.com,
	liran.alon@oracle.com, jwadams@google.com
Subject: Re: [RFC KVM 19/27] kvm/isolation: initialize the KVM page table with core mappings
Date: Mon, 13 May 2019 18:47:09 +0200	[thread overview]
Message-ID: <463b86c8-e9a0-fc13-efa4-31df3aea8e54@oracle.com> (raw)
In-Reply-To: <a9198e28-abe1-b980-597e-2d82273a2c17@intel.com>



On 5/13/19 5:50 PM, Dave Hansen wrote:
>> +	/*
>> +	 * Copy the mapping for all the kernel text. We copy at the PMD
>> +	 * level since the PUD is shared with the module mapping space.
>> +	 */
>> +	rv = kvm_copy_mapping((void *)__START_KERNEL_map, KERNEL_IMAGE_SIZE,
>> +	     PGT_LEVEL_PMD);
>> +	if (rv)
>> +		goto out_uninit_page_table;
> 
> Could you double-check this?  We (I) have had some repeated confusion
> with the PTI code and kernel text vs. kernel data vs. __init.
> KERNEL_IMAGE_SIZE looks to be 512MB which is quite a bit bigger than
> kernel text.

I probably have the same confusion :-) but I will try to check again.


>> +	/*
>> +	 * Copy the mapping for cpu_entry_area and %esp fixup stacks
>> +	 * (this is based on the PTI userland address space, but probably
>> +	 * not needed because the KVM address space is not directly
>> +	 * enterered from userspace). They can both be copied at the P4D
>> +	 * level since they each have a dedicated P4D entry.
>> +	 */
>> +	rv = kvm_copy_mapping((void *)CPU_ENTRY_AREA_PER_CPU, P4D_SIZE,
>> +	     PGT_LEVEL_P4D);
>> +	if (rv)
>> +		goto out_uninit_page_table;
> 
> cpu_entry_area is used for more than just entry from userspace.  The gdt
> mapping, for instance, is needed everywhere.  You might want to go look
> at 'struct cpu_entry_area' in some more detail.

Ok. Thanks.

>> +#ifdef CONFIG_X86_ESPFIX64
>> +	rv = kvm_copy_mapping((void *)ESPFIX_BASE_ADDR, P4D_SIZE,
>> +	     PGT_LEVEL_P4D);
>> +	if (rv)
>> +		goto out_uninit_page_table;
>> +#endif
> 
> Why are these mappings *needed*?  I thought we only actually used these
> fixup stacks for some crazy iret-to-userspace handling.  We're certainly
> not doing that from KVM context.

Right. I initially looked what was used for PTI, and I probably copied unneeded
mapping.

> Am I forgetting something?
> 
>> +#ifdef CONFIG_VMAP_STACK
>> +	/*
>> +	 * Interrupt stacks are vmap'ed with guard pages, so we need to
>> +	 * copy mappings.
>> +	 */
>> +	for_each_possible_cpu(cpu) {
>> +		stack = per_cpu(hardirq_stack_ptr, cpu);
>> +		pr_debug("IRQ Stack %px\n", stack);
>> +		if (!stack)
>> +			continue;
>> +		rv = kvm_copy_ptes(stack - IRQ_STACK_SIZE, IRQ_STACK_SIZE);
>> +		if (rv)
>> +			goto out_uninit_page_table;
>> +	}
>> +
>> +#endif
> 
> I seem to remember that the KVM VMENTRY/VMEXIT context is very special.
>   Interrupts (and even NMIs?) are disabled.  Would it be feasible to do
> the switching in there so that we never even *get* interrupts in the KVM
> context?

Ideally we would like to run with the KVM address space when handling a VM-exit
(so between a VMEXIT and the next VMENTER) where interrupts are not disabled.

> I also share Peter's concerns about letting modules do this.  If we ever
> go down this road, we're going to have to think very carefully how we
> let KVM do this without giving all the not-so-nice out-of-tree modules
> the keys to the castle.

Right, we probably need some more generic framework for creating limited
kernel context space which kvm (or other module?) can deal with. I think
kvm is a good place to start for having this kind of limited context, hence
this RFC and my request for advice how best to do it.

> A high-level comment: it looks like this is "working", but has probably
> erred on the side of mapping too much.  The hard part is paring this
> back to a truly minimal set of mappings.
> 

Agree.

Thanks,

alex.

  parent reply	other threads:[~2019-05-13 16:48 UTC|newest]

Thread overview: 86+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-13 14:38 [RFC KVM 00/27] KVM Address Space Isolation Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 01/27] kernel: Export memory-management symbols required for KVM address space isolation Alexandre Chartre
2019-05-13 15:15   ` Peter Zijlstra
2019-05-13 15:17     ` Liran Alon
2019-05-13 14:38 ` [RFC KVM 02/27] KVM: x86: Introduce address_space_isolation module parameter Alexandre Chartre
2019-05-13 15:46   ` Andy Lutomirski
2019-05-13 15:55     ` Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 03/27] KVM: x86: Introduce KVM separate virtual address space Alexandre Chartre
2019-05-13 15:45   ` Andy Lutomirski
2019-05-13 16:04     ` Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 04/27] KVM: x86: Switch to KVM address space on entry to guest Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 05/27] KVM: x86: Add handler to exit kvm isolation Alexandre Chartre
2019-05-13 15:49   ` Andy Lutomirski
2019-05-13 16:10     ` Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 06/27] KVM: x86: Exit KVM isolation on IRQ entry Alexandre Chartre
2019-05-13 15:51   ` Andy Lutomirski
2019-05-13 16:28     ` Alexandre Chartre
2019-05-13 18:13       ` Andy Lutomirski
2019-05-14  7:07         ` Peter Zijlstra
2019-05-14  7:58           ` Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 07/27] KVM: x86: Switch to host address space when may access sensitive data Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 08/27] KVM: x86: Optimize branches which checks if address space isolation enabled Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 09/27] kvm/isolation: function to track buffers allocated for the KVM page table Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 10/27] kvm/isolation: add KVM page table entry free functions Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 11/27] kvm/isolation: add KVM page table entry offset functions Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 12/27] kvm/isolation: add KVM page table entry allocation functions Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 13/27] kvm/isolation: add KVM page table entry set functions Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 14/27] kvm/isolation: functions to copy page table entries for a VA range Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 15/27] kvm/isolation: keep track of VA range mapped in KVM address space Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 16/27] kvm/isolation: functions to clear page table entries for a VA range Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 17/27] kvm/isolation: improve mapping copy when mapping is already present Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 18/27] kvm/isolation: function to copy page table entries for percpu buffer Alexandre Chartre
2019-05-13 18:18   ` Andy Lutomirski
2019-05-14  7:09     ` Peter Zijlstra
2019-05-14  8:25       ` Alexandre Chartre
2019-05-14  8:34         ` Andy Lutomirski
2019-05-14  9:41           ` Alexandre Chartre
2019-05-14 15:23             ` Andy Lutomirski
2019-05-14 16:24               ` Alexandre Chartre
2019-05-14 17:05                 ` Peter Zijlstra
2019-05-14 18:09                   ` Sean Christopherson
2019-05-14 20:33                     ` Andy Lutomirski
2019-05-14 21:06                       ` Sean Christopherson
2019-05-14 21:55                         ` Andy Lutomirski
2019-05-14 22:38                           ` Sean Christopherson
2019-05-18  0:05                             ` Jonathan Adams
2019-05-14 20:27                   ` Andy Lutomirski
2019-05-13 14:38 ` [RFC KVM 19/27] kvm/isolation: initialize the KVM page table with core mappings Alexandre Chartre
2019-05-13 15:50   ` Dave Hansen
2019-05-13 16:00     ` Andy Lutomirski
2019-05-13 17:00       ` Alexandre Chartre
2019-05-13 16:46     ` Sean Christopherson
2019-05-13 16:47     ` Alexandre Chartre [this message]
2019-05-14 10:26       ` Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 20/27] kvm/isolation: initialize the KVM page table with vmx specific data Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 21/27] kvm/isolation: initialize the KVM page table with vmx VM data Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 22/27] kvm/isolation: initialize the KVM page table with vmx cpu data Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 23/27] kvm/isolation: initialize the KVM page table with the vcpu tasks Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 24/27] kvm/isolation: KVM page fault handler Alexandre Chartre
2019-05-13 15:15   ` Peter Zijlstra
2019-05-13 21:25     ` Liran Alon
2019-05-14  2:02       ` Andy Lutomirski
2019-05-14  7:21         ` Peter Zijlstra
2019-05-14 15:36           ` Alexandre Chartre
2019-05-14 15:43             ` Andy Lutomirski
2019-05-13 16:02   ` Andy Lutomirski
2019-05-13 16:21     ` Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 25/27] kvm/isolation: implement actual KVM isolation enter/exit Alexandre Chartre
2019-05-13 15:16   ` Peter Zijlstra
2019-05-13 16:01   ` Andy Lutomirski
2019-05-13 14:38 ` [RFC KVM 26/27] kvm/isolation: initialize the KVM page table with KVM memslots Alexandre Chartre
2019-05-13 14:38 ` [RFC KVM 27/27] kvm/isolation: initialize the KVM page table with KVM buses Alexandre Chartre
2019-05-13 16:42 ` [RFC KVM 00/27] KVM Address Space Isolation Liran Alon
2019-05-13 18:17 ` Andy Lutomirski
2019-05-13 21:08   ` Liran Alon
2019-05-14  2:07     ` Andy Lutomirski
2019-05-14  7:37       ` Peter Zijlstra
2019-05-14 21:32         ` Jan Setje-Eilers
2019-05-14  8:05       ` Liran Alon
2019-05-14  7:29     ` Peter Zijlstra
2019-05-14  7:57       ` Liran Alon
2019-05-14  8:33     ` Alexandre Chartre
2019-05-13 19:31 ` Nakajima, Jun
2019-05-13 21:16   ` Liran Alon
     [not found]     ` <D07C8F51-F2DF-4C8B-AB3B-0DFABD5F4C33@intel.com>
2019-05-13 21:53       ` Liran Alon
2019-05-15 12:52 ` Alexandre Chartre

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