linux-kernel - Re: [Xen-devel] [PATCH 02/13] xen: anchor linear p2m list in shared info structure

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 18 Feb 2015 10:50:09 +0000
From:	Andrew Cooper <andrew.cooper3@...rix.com>
To:	Juergen Gross <jgross@...e.com>,
	David Vrabel <david.vrabel@...rix.com>,
	<linux-kernel@...r.kernel.org>, <xen-devel@...ts.xensource.com>,
	<konrad.wilk@...cle.com>, <boris.ostrovsky@...cle.com>
Subject: Re: [Xen-devel] [PATCH 02/13] xen: anchor linear p2m list in shared
 info structure

On 18/02/15 10:42, Juergen Gross wrote:
>
>>>   /* Set up p2m_top to point to the domain-builder provided p2m
>>> pages */
>>> @@ -469,8 +473,10 @@ static pte_t *alloc_p2m_pmd(unsigned long addr,
>>> pte_t *pte_pg)
>>>
>>>           ptechk = lookup_address(vaddr, &level);
>>>           if (ptechk == pte_pg) {
>>> +            HYPERVISOR_shared_info->arch.p2m_generation++;
>>>               set_pmd(pmdp,
>>>                   __pmd(__pa(pte_newpg[i]) | _KERNPG_TABLE));
>>> +            HYPERVISOR_shared_info->arch.p2m_generation++;
>>
>> Do these increments of p2m_generation need to be atomic?
>
> Hmm, they are done under lock. I don't think the compiler is allowed to
> reorder the writes to p2m_generation across set_pmd().

They do need smp_wmb() to guarantee that the increment is visible before
the update occurs, just as the toolstack will need smp_rmb() to read.

They also need to be protected from concurrent update inside the kernel,
for which a lock should appear to suffice.

~Andrew

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/