linux-kernel - Re: [PATCH 2/4] xen/lowlevel: Implement pvop call for load

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Message-ID: <20121018144538.GA19782@localhost.localdomain>
Date:	Thu, 18 Oct 2012 10:45:41 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	lenb@...nel.org, linux-acpi@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 2/4] xen/lowlevel: Implement pvop call for load_idt
 (sidt).

On Wed, Oct 17, 2012 at 04:51:17PM -0700, H. Peter Anvin wrote:
> On 10/17/2012 06:49 AM, Konrad Rzeszutek Wilk wrote:
> >In the past it used to point to 'sidt' (native_store_idt) operation
> >which is a non-privileged operation. This resulted in the
> >'struct desc_ptr' value containing the address of Xen's IDT table,
> >instead of the IDT table that Linux thinks its using. The end result
> >is that doing:
> >
> >   store_idt(&desc);
> >   load_idt(&desc);
> >
> >would blow up b/c xen_load_idt would try to parse the IDT contents
> >(desc) and de-reference a virtual address that is outside Linux's
> >__va (it is in Xen's virtual address).
> >
> >With this patch we are providing the last written IDT address.
> >
> 
> OK... this seems like another excellent set of pvops calls that
> should be nukable to Kingdom Come.  There is no reason, ever, to
> read the IDT and GDT from the kernel... the kernel already knows
> what they should be!

Even during suspend and resume cycle? There are the sequence of
sidt/lidt calls being done there. And we do need to filter at
least the sidt call - and in the case of ACPI suspend path,
the lidt.
> 
> 	-hpa
> 
> 
> -- 
> H. Peter Anvin, Intel Open Source Technology Center
> I work for Intel.  I don't speak on their behalf.
> 
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