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From: Alexandre Chartre <alexandre.chartre@oracle.com>
To: Andy Lutomirski <luto@kernel.org>, Dave Hansen <dave.hansen@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Radim Krcmar <rkrcmar@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	kvm list <kvm@vger.kernel.org>, X86 ML <x86@kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	jan.setjeeilers@oracle.com, Liran Alon <liran.alon@oracle.com>,
	Jonathan Adams <jwadams@google.com>
Subject: Re: [RFC KVM 19/27] kvm/isolation: initialize the KVM page table with core mappings
Date: Mon, 13 May 2019 19:00:31 +0200	[thread overview]
Message-ID: <ec26a85f-ff1c-89d9-5e6c-ff42e834c48d@oracle.com> (raw)
In-Reply-To: <CALCETrXYW-CfixanL3Wk5v_5Ex7WMe+7POV0VfBVHujfb6cvtQ@mail.gmail.com>



On 5/13/19 6:00 PM, Andy Lutomirski wrote:
> On Mon, May 13, 2019 at 8:50 AM Dave Hansen <dave.hansen@intel.com> 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.
>>
>>> +     /*
>>> +      * 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.
>>
>>> +#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.
>>
>> 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?
> 
> That would be nicer.
> 
> Looking at this code, it occurs to me that mapping the IRQ stacks
> seems questionable.  As it stands, this series switches to a normal
> CR3 in some C code somewhere moderately deep in the APIC IRQ code.  By
> that time, I think you may have executed traceable code, and, if that
> happens, you lose.  i hate to say this, but any shenanigans like this
> patch does might need to happen in the entry code *before* even
> switching to the IRQ stack.  Or perhaps shortly thereafter.
>
> We've talked about moving context tracking to C.  If we go that route,
> then this KVM context mess could go there, too -- we'd have a
> low-level C wrapper for each entry that would deal with getting us
> ready to run normal C code.
> 
> (We need to do something about terminology.  This kvm_mm thing isn't
> an mm in the normal sense.  An mm has normal kernel mappings and
> varying user mappings.  For example, the PTI "userspace" page tables
> aren't an mm.  And we really don't want a situation where the vmalloc
> fault code runs with the "kvm_mm" mm active -- it will totally
> malfunction.)
> 

One of my next step is to try to put the KVM page table in the PTI userspace
page tables, and not switch CR3 on KVM_RUN ioctl. That way, we will run with
a regular mm (but using the userspace page table). Then interrupt would switch
CR3 to kernel page table (like paranoid idtentry currently do it).

alex.





  reply	other threads:[~2019-05-13 17:02 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 [this message]
2019-05-13 16:46     ` Sean Christopherson
2019-05-13 16:47     ` Alexandre Chartre
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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