From: Jan Beulich <jbeulich@suse.com>
To: "Andrew Cooper" <andrew.cooper3@citrix.com>,
"Roger Pau Monné" <roger.pau@citrix.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
Wei Liu <wl@xen.org>
Subject: Ping: [PATCH] x86/PV: make post-migration page state consistent
Date: Fri, 16 Oct 2020 12:21:26 +0200 [thread overview]
Message-ID: <f4804dc9-4a6f-6601-2fc9-9b6d4a3ae41a@suse.com> (raw)
In-Reply-To: <f7ed53c1-768c-cc71-a432-553b56f7f0a7@suse.com>
On 11.09.2020 12:34, Jan Beulich wrote:
> When a page table page gets de-validated, its type reference count drops
> to zero (and PGT_validated gets cleared), but its type remains intact.
> XEN_DOMCTL_getpageframeinfo3, therefore, so far reported prior usage for
> such pages. An intermediate write to such a page via e.g.
> MMU_NORMAL_PT_UPDATE, however, would transition the page's type to
> PGT_writable_page, thus altering what XEN_DOMCTL_getpageframeinfo3 would
> return. In libxc the decision which pages to normalize / localize
> depends solely on the type returned from the domctl. As a result without
> further precautions the guest won't be able to tell whether such a page
> has had its (apparent) PTE entries transitioned to the new MFNs.
>
> Add a check of PGT_validated, thus consistently avoiding normalization /
> localization in the tool stack.
>
> Alongside using XEN_DOMCTL_PFINFO_NOTAB instead of plain zero for the
> change at hand, also change the variable's initializer to use this
> constant, too. Take the opportunity and also adjust its type.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
I think I did address all questions here.
Jan
> --- a/xen/arch/x86/domctl.c
> +++ b/xen/arch/x86/domctl.c
> @@ -215,7 +215,8 @@ long arch_do_domctl(
>
> for ( i = 0; i < num; ++i )
> {
> - unsigned long gfn = 0, type = 0;
> + unsigned long gfn = 0;
> + unsigned int type = XEN_DOMCTL_PFINFO_NOTAB;
> struct page_info *page;
> p2m_type_t t;
>
> @@ -255,6 +256,8 @@ long arch_do_domctl(
>
> if ( page->u.inuse.type_info & PGT_pinned )
> type |= XEN_DOMCTL_PFINFO_LPINTAB;
> + else if ( !(page->u.inuse.type_info & PGT_validated) )
> + type = XEN_DOMCTL_PFINFO_NOTAB;
>
> if ( page->count_info & PGC_broken )
> type = XEN_DOMCTL_PFINFO_BROKEN;
>
next prev parent reply other threads:[~2020-10-16 10:21 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-11 10:34 [PATCH] x86/PV: make post-migration page state consistent Jan Beulich
2020-09-11 11:55 ` Andrew Cooper
2020-09-11 12:37 ` Jan Beulich
2020-09-28 12:16 ` Jan Beulich
2020-10-16 10:21 ` Jan Beulich [this message]
2020-10-29 13:53 ` Ping²: " Jan Beulich
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