From mboxrd@z Thu Jan  1 00:00:00 1970
From: tgh <tianguanhua@ncic.ac.cn>
Subject: Re: confused about the balloon code
Date: Sat, 28 Apr 2007 17:06:16 +0800
Message-ID: <46330E88.90201@ncic.ac.cn>
References: <C258C16F.67E4%Keir.Fraser@cl.cam.ac.uk>
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To: Keir Fraser <Keir.Fraser@cl.cam.ac.uk>
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Thank you for your reply

and I have got other confusions in function of increase_reservation() as=20
follows :
static int increase_reservation(unsigned long nr_pages)
{
....
page =3D balloon_first_page();
for (i =3D 0; i < nr_pages; i++) {
BUG_ON(page =3D=3D NULL);
////**********************************
frame_list[i] =3D page_to_pfn(page);;
////*********** my confusion
////***********frame_list[i] is set by a pfn, while in the later part of=20
this function and in decrease_reservation() ,frame_list[i] is set by=20
mfn,is it right?
////*********** if it is , what is the trick behind it?
////************************************

page =3D balloon_next_page(page);
}

set_xen_guest_handle(reservation.extent_start, frame_list);
reservation.nr_extents =3D nr_pages;
////**********************************************
rc =3D HYPERVISOR_memory_op(
XENMEM_populate_physmap, &reservation);
////************************another confusion
////************************what is the function of=20
XENMEM_populate_physmap hypercall?
////************************ is it to allocate the mfn for the guestOS=20
and at that time ,the frame_list[i] is mfn not the pfn as above , or=20
what is the function?
////**************************************************

....

for (i =3D 0; i < nr_pages; i++) {
page =3D balloon_retrieve();
BUG_ON(page =3D=3D NULL);

pfn =3D page_to_pfn(page);
BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
phys_to_machine_mapping_valid(pfn));

/* Update P->M and M->P tables. */
set_phys_to_machine(pfn, frame_list[i]);
xen_machphys_update(frame_list[i], pfn);

/* Link back into the page tables if not highmem. */
if (pfn < max_low_pfn) {
int ret;
////********************************************************
ret =3D HYPERVISOR_update_va_mapping(
(unsigned long)__va(pfn << PAGE_SHIFT),
pfn_pte_ma(frame_list[i], PAGE_KERNEL),
0);
////***********************another confustion
////***********************what is the function of this hypercall?
////*********************** I am totally confused about it
////********************************************************
BUG_ON(ret);
}

/* Relinquish the page back to the allocator. */
ClearPageReserved(page);
set_page_count(page, 1);
__free_page(page);
}
...
}

I am confused about it
could you help me
Thanks in advance










Keir Fraser =E5=86=99=E9=81=93:
> On 28/4/07 02:13, "tgh" <tianguanhua@ncic.ac.cn> wrote:
>
>  =20
>> I am confused about the scrub_pages(), what is the meaning of
>> scrub_pages, when should we use CONFIG_XEN_SCRUB_PAGES
>> could you help me
>>    =20
>
> It causes the guest to zero out pages that it gives back to Xen. It's a
> security option.
>
>  -- Keir
>
>
>
>
>  =20