From: Denys Vlasenko <dvlasenk@redhat.com>
To: "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@kernel.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
David Vrabel <david.vrabel@citrix.com>,
Joerg Roedel <joro@8bytes.org>, Gleb Natapov <gleb@kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, x86@kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled
Date: Sat, 26 Sep 2015 22:38:25 +0200 [thread overview]
Message-ID: <56070241.2030407@redhat.com> (raw)
In-Reply-To: <706E9982-24E3-442B-808A-172909449DD4@zytor.com>
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 <dvlasenk@redhat.com> wrote:
>> 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, other writes nearby will cause
>> those faults too.
>>
>> In other words, we need GDT to live in a separate page
>> only if CONFIG_HYPERVISOR_GUEST=y.
>>
>> This patch reduces GDT alignment to cacheline-aligned
>> if CONFIG_HYPERVISOR_GUEST is not set.
>>
>> Patch also renames gdt_page to cpu_gdt (mimicking naming of existing
>> cpu_tss per-cpu variable), since now it is not always a full page.
next prev parent reply other threads:[~2015-09-26 20:38 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-26 18:00 [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled Denys Vlasenko
2015-09-26 19:50 ` H. Peter Anvin
2015-09-26 20:38 ` Denys Vlasenko [this message]
2015-09-28 7:58 ` Ingo Molnar
2015-09-28 12:45 ` Denys Vlasenko
2015-09-29 9:01 ` Ingo Molnar
2015-09-29 17:35 ` Andy Lutomirski
2015-09-29 17:50 ` Linus Torvalds
2015-09-29 18:02 ` Andy Lutomirski
2015-09-29 20:30 ` H. Peter Anvin
2015-09-30 1:20 ` Eric W. Biederman
2015-09-30 1:31 ` H. Peter Anvin
2015-09-30 2:11 ` Eric W. Biederman
2015-09-30 2:26 ` H. Peter Anvin
2015-09-29 18:18 ` H. Peter Anvin
2015-09-29 18:22 ` Andy Lutomirski
2015-09-29 18:27 ` H. Peter Anvin
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