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Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system
From: |
Xu, Anthony |
Subject: |
Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode |
Date: |
Thu, 11 May 2017 23:55:11 +0000 |
Hi Paolo,
In KVM mode, seems A20 is ignored.
Do you see any potential issue here?
Anthony
> -----Original Message-----
> From: Kevin O'Connor [mailto:address@hidden
> Sent: Thursday, May 11, 2017 9:35 AM
> To: Paolo Bonzini <address@hidden>
> Cc: address@hidden; Xu, Anthony <address@hidden>
> Subject: Re: [PATCH] target/i386: enable A20 automatically in system
> management mode
>
> 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, 2017/05/11
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode,
Xu, Anthony <=
- 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
- Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode, Kevin O'Connor, 2017/05/16