linux-kernel - Re: [PATCH 1/2] xen/granttable: Support sub-page grants

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]

Message-ID: <4EDE4EC4.8070802@goop.org>
Date:	Tue, 06 Dec 2011 09:20:04 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ian Campbell <Ian.Campbell@...rix.com>
CC:	"annie.li@...cle.com" <annie.li@...cle.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"kurt.hackel@...cle.com" <kurt.hackel@...cle.com>,
	Paul Durrant <Paul.Durrant@...rix.com>
Subject: Re: [PATCH 1/2] xen/granttable: Support sub-page grants

On 12/06/2011 03:42 AM, Ian Campbell wrote:
>> +{
>> +	int ref;
>> +
>> +	ref = get_free_entries(1);
>> +	if (unlikely(ref < 0))
>> +		return -ENOSPC;
>> +
>> +	gnttab_grant_foreign_access_ref_subpage_v2(ref, domid, frame, flags,
>> +						   page_off, length);
>> +
>> +	return ref;
>> +}
>> +EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_subpage_v2);
>> +
>> +void gnttab_grant_foreign_access_ref_subpage_v2(grant_ref_t ref, domid_t domid,
>> +						unsigned long frame, int flags,
>> +						unsigned page_off,
>> +						unsigned length)
>> +{
>> +	BUG_ON(flags & (GTF_accept_transfer | GTF_reading |
>> +			GTF_writing | GTF_transitive));
>> +	BUG_ON(grant_table_version == 1);
> Returning -Esomething might be less drastic? ENOSYS perhaps?

Yeah, BUG_ON shouldn't be used for API misuse unless there's absolutely
no other way to handle it.

>
>> +	gnttab_shared.v2[ref].sub_page.frame = frame;
>> +	gnttab_shared.v2[ref].sub_page.page_off = page_off;
>> +	gnttab_shared.v2[ref].sub_page.length = length;
>> +	gnttab_shared.v2[ref].hdr.domid = domid;
>> +	wmb();
>> +	gnttab_shared.v2[ref].hdr.flags =
>> +				GTF_permit_access | GTF_sub_page | flags;
>> +}
>> +EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_ref_subpage_v2);
>> +
>> +bool gnttab_subpage_trans_grants_available(void)
>> +{
>> +	return grant_table_version == 2;
>> +}
> It's not clear this adds anything over and above letting the user query
> the grant table version. It's hard to tell since there are no users
> presented here though. Perhaps separate subpage and transitive functions
> would be cleaner?

Well, in general, specifically testing for features rather than
interface versions is better.

    J
--
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/