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From: Kevin O'Connor <kevin@koconnor.net>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org, anthony.xu@intel.com
Subject: Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode
Date: Thu, 11 May 2017 10:53:12 -0400	[thread overview]
Message-ID: <20170511145312.GA822@morn.lan> (raw)
In-Reply-To: <1494502528-12670-1-git-send-email-pbonzini@redhat.com>

On Thu, May 11, 2017 at 01:35:28PM +0200, Paolo Bonzini wrote:
> Ignore env->a20_mask when running in system management mode.

Thanks Paolo.  I don't think this patch will help SeaBIOS though.  The
SeaBIOS SMM handler doesn't do much - it doesn't even access ram above
1MiB.  See SeaBIOS' code in src/fw/smm.c:handle_smi().

Instead, the SeaBIOS code does a cpu state backup/restore to switch
into 32bit mode.  I thought the A20 state would be part of that cpu
backup/restore.  However, looking at the Intel SDM docs now, it's not
really clear to me how the processor "inhibits" A20 when in SMM mode -
does it save/restore that state on SMI/RSM or does it have special
logic to ignore A20 while in SMM mode?

-Kevin

  parent reply	other threads:[~2017-05-11 14:53 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-05-11 11:35 [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode Paolo Bonzini
2017-05-11 11:41 ` no-reply
2017-05-11 11:58 ` no-reply
2017-05-11 14:53 ` Kevin O'Connor [this message]
2017-05-11 15:32   ` Paolo Bonzini
2017-05-11 16:34     ` Kevin O'Connor
2017-05-11 23:55       ` Xu, Anthony
2017-05-12 12:16         ` Paolo Bonzini
2017-05-12 18:55           ` Xu, Anthony
2017-05-12 19:16             ` Paolo Bonzini
2017-05-12 19:38               ` Kevin O'Connor
2017-05-12 23:19                 ` Xu, Anthony
2017-05-13  0:01                   ` Kevin O'Connor
2017-05-13  1:24                     ` Xu, Anthony
2017-05-16 16:24                       ` Kevin O'Connor
2017-05-16 20:00                         ` Xu, Anthony
2017-05-16 21:42                           ` Kevin O'Connor
2017-05-16 22:39                             ` Xu, Anthony
2017-05-17  8:18                             ` Paolo Bonzini

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