linux-kernel - Re: [Xen-devel] [PATCH 4/8] xen/pvh: Bootstrap PVH guest

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Message-ID: <f8199e1a-0bef-61ff-8cad-e1713c9f10a3@citrix.com>
Date:   Fri, 14 Oct 2016 20:12:03 +0100
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        <david.vrabel@...rix.com>, <JGross@...e.com>
CC:     Matt Fleming <matt@...eblueprint.co.uk>,
        <xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>,
        <roger.pau@...rix.com>
Subject: Re: [Xen-devel] [PATCH 4/8] xen/pvh: Bootstrap PVH guest

On 14/10/16 19:55, Boris Ostrovsky wrote:
> On 10/14/2016 02:38 PM, Andrew Cooper wrote:
>>> +	jmp *%rax
>>> +
>>> +#else /* CONFIG_X86_64 */
>>> +
>>> +	call setup_pgtable_32
>>> +
>>> +	mov $_pa(initial_page_table), %eax
>>> +	movl %eax, %cr3
>>> +
>>> +	movl %cr0, %eax
>>> +	orl $(X86_CR0_PG | X86_CR0_PE), %eax
>>> +	movl %eax, %cr0
>>> +
>>> +	ljmp $__BOOT_CS,$1f
>>> +1:
>>> +	call xen_prepare_pvh
>> Why does xen_prepare_pvh need paging?  I can't spot anything which
>> should need it, and it feels conceptually wrong.
> xen_prepare_pvh() deals with virtual addresses. How can we run without paging?

Ah yes - with a high-half kernel, that way around doesn't work.  Sorry
for the noise - I have been spending too long working with virtual
addresses down round 0, where that specifically can be solved by setting
%ds with a suitable non-zero base.

~Andrew