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Subject: Re: [PATCH] kdump, vmcoreinfo: Export sme_me_mask value to vmcoreinfo
To:     Borislav Petkov <bp@alien8.de>, Petr Tesarik <ptesarik@suse.cz>
Cc:     linux-kernel@vger.kernel.org, bhe@redhat.com, x86@kernel.org,
        kexec@lists.infradead.org, mingo@redhat.com, tglx@linutronix.de,
        dyoung@redhat.com
References: <20181026093630.8520-1-lijiang@redhat.com>
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 <20181026182440.20a4b107@ezekiel.suse.cz>
 <20181026222517.GB26927@nazgul.tnic>
From:   lijiang <lijiang@redhat.com>
Message-ID: <a4bae45c-e52a-7fbb-6b74-5de12ea47368@redhat.com>
Date:   Sat, 27 Oct 2018 10:57:08 +0800
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在 2018年10月27日 06:25, Borislav Petkov 写道:
> On Fri, Oct 26, 2018 at 06:24:40PM +0200, Petr Tesarik wrote:
>> But we need the MSR value from the panic kernel environment, not while
>> the production kernel is still running, right?
> 
> Actually, we need only the encryption bit number (and it should be 0
> otherwise to denote SME wasn't enabled).
> 

Thanks for your comment.
For this patch, it really needs only the encryption bit number. 

For the AMD machine with SME feature, the OS or HV sets bit 47 of a
physical address to 1 in the page table entry to indicate the page
should be encrypted.

Thanks.
Lianbo

> I guess something like
> 
> 	VMCOREINFO_NUMBER(sme_mask);
> 
> which gets written by the kexec-ed kernel.
> 
>> If so, then this reminds me that I have wanted for a long time to store
>> more of the hardware state in a vmcore NOTE after a kernel crash ...
>> control registers, MSRs and whatnot. Of course, this would be a
>> long-term project, but I wonder what other people think about it in
>> general.
> 
> I guess that sounds like a good idea - the more relevant hw info for
> debugging, the better. Determining the important MSRs to save would need
> a bit of a pondering over though. For example, some MSRs are per-core,
> some per-socket, etc...
>