qemu-devel
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [SeaBIOS] [Qemu-devel] [RFC] Passing boot order from qemu to seabios


From: H. Peter Anvin
Subject: Re: [SeaBIOS] [Qemu-devel] [RFC] Passing boot order from qemu to seabios
Date: Mon, 11 Oct 2010 14:51:40 -0700
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.9) Gecko/20100921 Fedora/3.1.4-1.fc13 Thunderbird/3.1.4

On 10/11/2010 02:41 PM, Sebastian Herbszt wrote:
> H. Peter Anvin wrote:
>> On 10/11/2010 01:30 PM, Anthony Liguori wrote:
>>> On 10/11/2010 02:59 PM, Gleb Natapov wrote:
>>>> No boot rom should do that. extboot wreaks havoc when it is used.
>>>> And since virtio is now supported by bios there is no reason to use it.
>>>
>>> You don't really have a choice.  You could be doing hardware passthrough 
>>> and the ROM on the card may hijack int19.
>>
>> The BBS standard actually documents how to deal with that -- it pretty
>> much works out to "let the card initialize, then see if it mucked with
>> int19, and then put int19 back... if we want to run that card, then we
>> invoke the int19 that the card set up."
> 
> The BIOS Boot Specification, Version 1.01 from January 11, 1996 seems not to
> recommend this:
> 
> 3.4 Legacy IPL Devices
> 
> "Legacy IPL devices will be allowed to take control of the system (via hooking
> interrupts) in both Legacy and PnP systems. The Plug and Play BIOS 
> specification
> recommends that Legacy devices that hook a bootstrap interrupt such as INT 
> 19h, 18h,
> or 13h have the interrupt re-captured by the BIOS. This is not done because 
> grabbing
> an interrupt vector back after a device has hooked it can produce 
> unpredictable results.
> Further, by allowing the card to take control, the behavior of these Legacy 
> cards will
> be the same on both PnP and Legacy machines."
> 
> 6.8 Notes on the POST Process
> 
> "The Plug and Play BIOS Specification says that if a Legacy IPL device's 
> option
> ROM captures INT 18h or INT 19h, the BIOS should save this vector and then
> restore the original one put there by the BIOS. The BIOS Boot Specification
> deviates from this in that these vectors are not recaptured after each Legacy 
> option
> ROM returns from initialization. That would be considered unsafe."
> 

Sorry, you're right -- I confused the PNPBIOS spec with the BBS spec
(and compounded the error by correctly remembering that BBS overrides
PNPBIOS).

        -hpa



reply via email to

[Prev in Thread] Current Thread [Next in Thread]