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Re: [Xen-devel] [PATCH v3 4/4] KVM: VMX: Simplify segment_base
- To: Thomas Garnier <thgarnie@xxxxxxxxxx>
- From: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
- Date: Mon, 20 Feb 2017 08:56:35 -0800
- Cc: "linux-efi@xxxxxxxxxxxxxxx" <linux-efi@xxxxxxxxxxxxxxx>, Stanislaw Gruszka <sgruszka@xxxxxxxxxx>, kvm list <kvm@xxxxxxxxxxxxxxx>, Radim Krčmář <rkrcmar@xxxxxxxxxx>, Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>, Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>, Alexander Potapenko <glider@xxxxxxxxxx>, Pavel Machek <pavel@xxxxxx>, "H . Peter Anvin" <hpa@xxxxxxxxx>, Kernel Hardening <kernel-hardening@xxxxxxxxxxxxxxxxxx>, Jiri Olsa <jolsa@xxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxx>, Andi Kleen <ak@xxxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Michael Ellerman <mpe@xxxxxxxxxxxxxx>, Joerg Roedel <joro@xxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, "Luis R . Rodriguez" <mcgrof@xxxxxxxxxx>, kasan-dev <kasan-dev@xxxxxxxxxxxxxxxx>, Christian Borntraeger <borntraeger@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>, Borislav Petkov <bp@xxxxxxx>, Len Brown <len.brown@xxxxxxxxx>, Rik van Riel <riel@xxxxxxxxxx>, Jiri Kosina <jikos@xxxxxxxxxx>, Kees Cook <keescook@xxxxxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, He Chen <he.chen@xxxxxxxxxxxxxxx>, Brian Gerst <brgerst@xxxxxxxxx>, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, lguest@xxxxxxxxxxxxxxxx, Andy Lutomirski <luto@xxxxxxxxxx>, Josh Poimboeuf <jpoimboe@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Adam Buchbinder <adam.buchbinder@xxxxxxxxx>, Dmitry Vyukov <dvyukov@xxxxxxxxxx>, Jim Mattson <jmattson@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>, Linux PM list <linux-pm@xxxxxxxxxxxxxxx>, "Rafael J . Wysocki" <rjw@xxxxxxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>, Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
- Delivery-date: Mon, 20 Feb 2017 16:57:19 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On Fri, Feb 17, 2017 at 2:01 PM, Thomas Garnier <thgarnie@xxxxxxxxxx> wrote:
> On Fri, Feb 17, 2017 at 1:00 PM, Jim Mattson <jmattson@xxxxxxxxxx> wrote:
>> On Fri, Feb 17, 2017 at 12:11 PM, Thomas Garnier <thgarnie@xxxxxxxxxx> wrote:
>>> On Fri, Feb 17, 2017 at 9:49 AM, Jim Mattson <jmattson@xxxxxxxxxx> wrote:
>>>>
>>>> Can we use the read-only GDT here? When expanding the virtual address
>>>> for 64-bit system descriptors, isn't it sufficient to check (d->s == 0
>>>> && d->type != 0)?
>>>
>>> We can use the readonly GDT but I think doesn't matter one or the
>>> other here. We have to check specific types for LDT or TSS, other
>>> values describe other entries (cf Intel volume 3, 3.5) (for example 14
>>> & 15 on 64-bits are for trap & interrupt gates).
>>
>> According to volume 3 of the SDM, section 3.5.2:
>>
>> The following system descriptors expand to 16 bytes:
>> — Call gate descriptors (see Section 5.8.3.1, “IA-32e Mode Call Gates”)
>> — IDT gate descriptors (see Section 6.14.1, “64-Bit Mode IDT”)
>> — LDT and TSS descriptors (see Section 7.2.3, “TSS Descriptor in 64-bit
>> mode”).
>>
>> All legal system descriptor types (except for 0: Upper 8 bytes of an 16-byte
>> descriptor) should get the high 32 bits of the base address from the next
>> 8-byte
>> descriptor.
>>
>
> Ok, then I will test an updated version next week.
>
I'm going to send out some preliminary patches that just get rid of
this problem entirely.
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