From: Zachary Amsden <zach@vmware.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Andrew Morton <akpm@osdl.org>, Chris Wright <chrisw@osdl.org>,
Linus Torvalds <torvalds@osdl.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Virtualization Mailing List <virtualization@lists.osdl.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Zwane Mwaikambo <zwane@arm.linux.org.uk>,
Martin Bligh <mbligh@mbligh.org>,
Pratap Subrahmanyam <pratap@vmware.com>,
Christopher Li <chrisl@vmware.com>,
"Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [PATCH 4/21] i386 Broken bios common
Date: Tue, 08 Nov 2005 04:48:06 -0800 [thread overview]
Message-ID: <43709E86.8010203@vmware.com> (raw)
In-Reply-To: <20051108071935.GB28201@elte.hu>
Ingo Molnar wrote:
>* Zachary Amsden <zach@vmware.com> wrote:
>
>
>
>> gdt = get_cpu_gdt_table(cpu);
>> save_desc_40 = gdt[0x40 / 8];
>>- gdt[0x40 / 8] = bad_bios_desc;
>>+ gdt[0x40 / 8] = gdt[GDT_ENTRY_BAD_BIOS_CACHE];
>>
>>
>>
>
>i like the cleanup, but wouldnt it be simpler to dedicate GDT entry #8
>to the 0x40 descriptor, and hence be compatible with such broken BIOSes
>by default? Right now entry #8 is taken up by TLS segment #2, but we
>could change GDT_ENTRY_TLS_MIN from 6 to 9 and push the TLS segments to
>entries 9,10,11. [ Could there be any buggy SMM code that relies on
>having something at 0x40? ]
>
>
I worry that there could be buggy userspace code that relies on having
selector 0x40 - notably Wine. So although I would like to make 0x40 the
default, can't be guaranteed.
SMM code is safe, since it gets SMRAM mapped in on entry and has
descriptor saved state so it can mess with tables as it sees fit without
worrying about restoring anything.
Zach
next prev parent reply other threads:[~2005-11-08 12:48 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-11-08 4:22 [PATCH 4/21] i386 Broken bios common Zachary Amsden
2005-11-08 7:19 ` Ingo Molnar
2005-11-08 12:48 ` Zachary Amsden [this message]
2005-11-08 12:57 ` Ingo Molnar
2005-11-08 15:06 ` Linus Torvalds
2005-11-08 15:16 ` H. Peter Anvin
2005-11-08 21:07 ` Zachary Amsden
2005-11-08 21:52 ` Zachary Amsden
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