linux-kernel - Re: [PATCH v2 4/9] xen/pvh: Bootstrap PVH guest

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Message-ID: <0ca64861-0695-df0b-6b86-a41f3e170722@oracle.com>
Date:   Fri, 3 Feb 2017 11:20:35 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     roger.pau@...rix.com, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/9] xen/pvh: Bootstrap PVH guest


>> +
>> +	__HEAD
>> +
>> +/* Entry point for PVH guests. */
> Could you add some comments about register conetnts at entry?

Reference to Xen's docs/misc/hvmlite.markdown would be sifficient?




>> +gdt:
>> +	.word	gdt_end - gdt
>> +	.long	_pa(gdt)
> This is a rather strange construct: the NULL descriptor of the
> GDT being used as space for lgdt operand.
>
>> +	.word	0
>> +	.quad	0x0000000000000000 /* NULL descriptor */
> And this comment is wrong: the NULL descriptor is at "gdt:".

I'll change it to:

gdt:
        .word   gdt_end - gdt_start
        .long   _pa(gdt_start)
        .word   0
gdt_start:
        .quad   0x0000000000000000 /* NULL descriptor */
        .quad   0x0000000000000000 /* reserved */
#ifdef CONFIG_X86_64
        .quad   0x00af9a000000ffff /* __KERNEL_CS */
#else
        .quad   0x00cf9a000000ffff /* __KERNEL_CS */
#endif
        .quad   0x00cf92000000ffff /* __KERNEL_DS */
gdt_end:


>
>> +#ifdef CONFIG_X86_64
>> +	.quad	0x00af9a000000ffff /* __KERNEL_CS */
> Mind adding comments about the semantics of those constants?
> Or use GDT_ENTRY() macro?
>
>> +#else
>> +	.quad	0x00cf9a000000ffff /* __KERNEL_CS */
>> +#endif
>> +	.quad	0x00cf92000000ffff /* __KERNEL_DS */
>> +gdt_end:
>> +
>> +	.bss
>> +	.balign 4
>> +early_stack:
>> +	.fill 16, 1, 0
> Is the stack size large enough? With a hypercall being executed in
> xen_prepare_pvh() I doubt this will be okay.

What do you think it should be then?

-boris