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Re: [Xen-devel] [PATCH v5 2/3] x86: Remap GDT tables in the Fixmap section
- To: Andy Lutomirski <luto@xxxxxxxxxxxxxx>, Thomas Garnier <thgarnie@xxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 9 Mar 2017 21:43:05 +0000
- Cc: Michal Hocko <mhocko@xxxxxxxx>, Stanislaw Gruszka <sgruszka@xxxxxxxxxx>, kvm list <kvm@xxxxxxxxxxxxxxx>, "linux-doc@xxxxxxxxxxxxxxx" <linux-doc@xxxxxxxxxxxxxxx>, Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>, Frederic Weisbecker <fweisbec@xxxxxxxxx>, Josh Poimboeuf <jpoimboe@xxxxxxxxxx>, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>, "linux-mm@xxxxxxxxx" <linux-mm@xxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxx>, Radim Krčmář <rkrcmar@xxxxxxxxxx>, "linux-efi@xxxxxxxxxxxxxxx" <linux-efi@xxxxxxxxxxxxxxx>, Alexander Potapenko <glider@xxxxxxxxxx>, Pavel Machek <pavel@xxxxxx>, "H . Peter Anvin" <hpa@xxxxxxxxx>, "kernel-hardening@xxxxxxxxxxxxxxxxxx" <kernel-hardening@xxxxxxxxxxxxxxxxxx>, Jiri Olsa <jolsa@xxxxxxxxxx>, zijun_hu <zijun_hu@xxxxxxx>, Prarit Bhargava <prarit@xxxxxxxxxx>, Andi Kleen <ak@xxxxxxxxxxxxxxx>, Len Brown <len.brown@xxxxxxxxx>, Jonathan Corbet <corbet@xxxxxxx>, Michael Ellerman <mpe@xxxxxxxxxxxxxx>, Joerg Roedel <joro@xxxxxxxxxx>, X86 ML <x86@xxxxxxxxxx>, "Luis R . Rodriguez" <mcgrof@xxxxxxxxxx>, kasan-dev <kasan-dev@xxxxxxxxxxxxxxxx>, Christian Borntraeger <borntraeger@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Borislav Petkov <bp@xxxxxxx>, Fenghua Yu <fenghua.yu@xxxxxxxxx>, 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>, Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>, lguest@xxxxxxxxxxxxxxxx, Andy Lutomirski <luto@xxxxxxxxxx>, Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Dmitry Vyukov <dvyukov@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Lorenzo Stoakes <lstoakes@xxxxxxxxx>, Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>, "linux-pm@xxxxxxxxxxxxxxx" <linux-pm@xxxxxxxxxxxxxxx>, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>, "Rafael J . Wysocki" <rjw@xxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, David Vrabel <david.vrabel@xxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>, Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
- Delivery-date: Thu, 09 Mar 2017 21:44:58 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On 09/03/2017 21:32, Andy Lutomirski wrote:
> On Mon, Mar 6, 2017 at 2:03 PM, Thomas Garnier <thgarnie@xxxxxxxxxx> wrote:
>
>> --- a/arch/x86/xen/enlighten.c
>> +++ b/arch/x86/xen/enlighten.c
>> @@ -710,7 +710,7 @@ static void load_TLS_descriptor(struct thread_struct *t,
>>
>> *shadow = t->tls_array[i];
>>
>> - gdt = get_cpu_gdt_table(cpu);
>> + gdt = get_cpu_gdt_rw(cpu);
>> maddr = arbitrary_virt_to_machine(&gdt[GDT_ENTRY_TLS_MIN+i]);
>> mc = __xen_mc_entry(0);
> Boris, is this right? I don't see why it wouldn't be, but Xen is special.
Under Xen PV, the GDT is already read-only at this point. (It is not
safe to let the guest have writeable access to system tables, so the
guest must relinquish write access to the frames wishing to be used as
LDTs or GDTs.)
The hypercall acts on the frame, not a virtual address, so either alias
should be fine here.
Under this new scheme, there will be two read-only aliases. I guess
this is easier to maintain the split consistently across Linux, than to
special case Xen PV because it doesn't need the second alias.
~Andrew
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