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Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system
From: |
Kevin O'Connor |
Subject: |
Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode |
Date: |
Thu, 11 May 2017 12:34:47 -0400 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
On Thu, May 11, 2017 at 05:32:47PM +0200, Paolo Bonzini wrote:
> On 11/05/2017 16:53, Kevin O'Connor wrote:
> > 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?
>
> There isn't any documented place for A20 in the state save map (I checked
> AMD's BIOS/Kernel Developer Guide which is pretty comprehensive), so I
> think the latter is more plausible. What I'm doing in this patch is
> ignoring A20 while in SMM mode.
Okay.
> Then you would have to add an A20 save/restore in handle_smi; since
> CALL32SMM_ENTERID should not nest, I think you can just do this:
Yes, that should be fine.
> --- a/src/fw/smm.c
> +++ b/src/fw/smm.c
> @@ -54,7 +54,8 @@ struct smm_layout {
> struct smm_state backup2;
> u8 stack[0x7c00];
> u64 codeentry;
> - u8 pad_8008[0x7df8];
> + u8 a20;
> + u8 pad_8009[0x7df7];
> struct smm_state cpu;
> };
In order to avoid mixing code and data in the same cache line we could
do this instead:
struct smm_layout {
struct smm_state backup1;
struct smm_state backup2;
- u8 stack[0x7c00];
+ u32 backup_a20;
+ u8 stack[0x8000 - sizeof(struct smm_state)*2 - sizeof(u32)];
u64 codeentry;
u8 pad_8008[0x7df8];
struct smm_state cpu;
Thanks,
-Kevin
- [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode, Paolo Bonzini, 2017/05/11
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode, no-reply, 2017/05/11
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode, no-reply, 2017/05/11
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode, Kevin O'Connor, 2017/05/11
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode, Paolo Bonzini, 2017/05/11
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode,
Kevin O'Connor <=
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode, Xu, Anthony, 2017/05/11
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode, Paolo Bonzini, 2017/05/12
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode, Xu, Anthony, 2017/05/12
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode, Paolo Bonzini, 2017/05/12
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode, Kevin O'Connor, 2017/05/12
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode, Xu, Anthony, 2017/05/12
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode, Kevin O'Connor, 2017/05/12
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode, Xu, Anthony, 2017/05/12
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode, Kevin O'Connor, 2017/05/16
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode, Xu, Anthony, 2017/05/16