Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

* Denys Vlasenko wrote: > On 09/28/2015 09:58 AM, Ingo Molnar wrote: > > > > * Denys Vlasenko wrote: > > > >> On 09/26/2015 09:50 PM, H. Peter Anvin wrote: > >>> NAK. We really should map the GDT read-only on all 64 bit systems, > >>> since we can't

Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

No, it is a natural result of an implemention which treats setting the A bit as an abnormal flow (e.g. in microcode as opposed to hardware). On September 29, 2015 7:11:59 PM PDT, ebied...@xmission.com wrote: >"H. Peter Anvin" writes: > >> On 09/29/2015 06:20 PM, Eric W.

Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

"H. Peter Anvin" writes: > On 09/29/2015 06:20 PM, Eric W. Biederman wrote: >> Linus Torvalds writes: >> >>> On Tue, Sep 29, 2015 at 1:35 PM, Andy Lutomirski >>> wrote: Does anyone know what happens if you stick a

Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

On 09/29/2015 06:20 PM, Eric W. Biederman wrote: > Linus Torvalds writes: > >> On Tue, Sep 29, 2015 at 1:35 PM, Andy Lutomirski wrote: >>> >>> Does anyone know what happens if you stick a non-accessed segment in >>> the GDT, map the GDT RO,

Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

Linus Torvalds writes: > On Tue, Sep 29, 2015 at 1:35 PM, Andy Lutomirski wrote: >> >> Does anyone know what happens if you stick a non-accessed segment in >> the GDT, map the GDT RO, and access it? > > You should get a #PF, as you guess, but

Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

On Tue, Sep 29, 2015 at 1:35 PM, Andy Lutomirski wrote: > > Does anyone know what happens if you stick a non-accessed segment in > the GDT, map the GDT RO, and access it? You should get a #PF, as you guess, but go ahead and test it if you want to make sure. We do something

Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

On Tue, Sep 29, 2015 at 10:50 AM, Linus Torvalds wrote: > On Tue, Sep 29, 2015 at 1:35 PM, Andy Lutomirski wrote: >> >> Does anyone know what happens if you stick a non-accessed segment in >> the GDT, map the GDT RO, and access it? > > You

Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

SGDT would be easy to use, and it is logical that it is faster since it reads an internal register. SIDT does too but unlike the GDT has a secondary limit (it can never be larger than 4096 bytes) and so all limits in the range 4095-65535 are exactly equivalent. Anything that causes a write to

Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

On Sep 29, 2015 2:01 AM, "Ingo Molnar" wrote: > > > * Denys Vlasenko wrote: > > > On 09/28/2015 09:58 AM, Ingo Molnar wrote: > > > > > > * Denys Vlasenko wrote: > > > > > >> On 09/26/2015 09:50 PM, H. Peter Anvin wrote: > > >>> NAK.

Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

On Tue, Sep 29, 2015 at 11:18 AM, H. Peter Anvin wrote: > SGDT would be easy to use, and it is logical that it is faster since it reads > an internal register. SIDT does too but unlike the GDT has a secondary limit > (it can never be larger than 4096 bytes) and so all limits in

Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

Ugh. Didn't realize that. On September 29, 2015 11:22:04 AM PDT, Andy Lutomirski wrote: >On Tue, Sep 29, 2015 at 11:18 AM, H. Peter Anvin wrote: >> SGDT would be easy to use, and it is logical that it is faster since >it reads an internal register. SIDT

Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

On 09/29/2015 11:02 AM, Andy Lutomirski wrote: > On Tue, Sep 29, 2015 at 10:50 AM, Linus Torvalds > wrote: >> On Tue, Sep 29, 2015 at 1:35 PM, Andy Lutomirski wrote: >>> >>> Does anyone know what happens if you stick a non-accessed segment in

Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

* Denys Vlasenko wrote: > On 09/26/2015 09:50 PM, H. Peter Anvin wrote: > > NAK. We really should map the GDT read-only on all 64 bit systems, > > since we can't hide the address from SLDT. Same with the IDT. > > Sorry, I don't understand your point. So the problem is

Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

On 09/28/2015 09:58 AM, Ingo Molnar wrote: > > * Denys Vlasenko wrote: > >> On 09/26/2015 09:50 PM, H. Peter Anvin wrote: >>> NAK. We really should map the GDT read-only on all 64 bit systems, >>> since we can't hide the address from SLDT. Same with the IDT. >> >> Sorry,

Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

On 09/26/2015 09:50 PM, H. Peter Anvin wrote: > NAK. We really should map the GDT read-only on all 64 bit systems, > since we can't hide the address from SLDT. Same with the IDT. Sorry, I don't understand your point. > On September 26, 2015 11:00:40 AM PDT, Denys Vlasenko

[PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

We have our GDT in a page-sized per-cpu structure, gdt_page. On x86_64 kernel, GDT is 128 bytes - only ~3% of that page is used. It is page-sized because of paravirt. Hypervisors need to know when GDT is changed, so they remap it read-only and handle write faults. If it's not in its own page,

Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

NAK. We really should map the GDT read-only on all 64 bit systems, since we can't hide the address from SLDT. Same with the IDT. On September 26, 2015 11:00:40 AM PDT, Denys Vlasenko wrote: >We have our GDT in a page-sized per-cpu structure, gdt_page. > >On x86_64