linux-kernel - Re: [PATCH 08/12] KVM: x86: save/load state on SMM switch

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Date:	Thu, 21 May 2015 18:23:31 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>
CC:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, bsd@...hat.com
Subject: Re: [PATCH 08/12] KVM: x86: save/load state on SMM switch



On 21/05/2015 18:20, Radim Krčmář wrote:
> 2. NMI -> SMI -> IRET -> RSM -> NMI
> NMI is injected;  I think it shouldn't be ... have you based this
> behavior on the 3rd paragraph of SDM 34.8 NMI HANDLING WHILE IN SMM
> ("A special case [...]")?

Yes.

> Why I think we should restore NMI mask on RSM:
> - It's consistent with SMI -> IRET -> NMI -> RSM -> NMI (where we,
>   I think correctly, unmask NMIs)

Yes, we do.

> and the idea that SMM tries to be to
>   transparent (but maybe they didn't care about retarded SMI handlers).

That's my reading of that paragraph of the manual. :)

> - APM 2:15.30.3 SMM_CTL MSR (C001_0116h)
>   • ENTER—Bit 1. Enter SMM: map the SMRAM memory areas, record whether
>     NMI was currently blocked and block further NMI and SMI interrupts.
>   • EXIT—Bit 3. Exit SMM: unmap the SMRAM memory areas, restore the
>     previous masking status of NMI and unconditionally reenable SMI.
>   
>   The MSR should mimic real SMM signals and does restore the NMI mask.

No idea...  My implementation does restore the previous masking status,
but only if it was "unmasked".

Paolo
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