From: Andrew Cooper <andrew.cooper3@citrix.com>
To: <paul@xen.org>, 'Xen-devel' <xen-devel@lists.xenproject.org>
Cc: "'George Dunlap'" <George.Dunlap@eu.citrix.com>,
"'Ian Jackson'" <iwj@xenproject.org>,
"'Jan Beulich'" <JBeulich@suse.com>,
"'Stefano Stabellini'" <sstabellini@kernel.org>,
"'Wei Liu'" <wl@xen.org>, "'Julien Grall'" <julien@xen.org>,
"'Michał Leszczyński'" <michal.leszczynski@cert.pl>,
"'Hubert Jasudowicz'" <hubert.jasudowicz@cert.pl>,
"'Tamas K Lengyel'" <tamas@tklengyel.com>
Subject: Re: [PATCH v2 04/11] xen/memory: Fix acquire_resource size semantics
Date: Thu, 24 Sep 2020 11:57:43 +0100 [thread overview]
Message-ID: <336c1114-2ffb-312c-0990-d2fa389a3b23@citrix.com> (raw)
In-Reply-To: <003b01d6925a$67f9e2b0$37eda810$@xen.org>
On 24/09/2020 11:06, Paul Durrant wrote:
>> diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
>> index d1cfc8fb4a..e82307bdae 100644
>> --- a/xen/arch/x86/mm.c
>> +++ b/xen/arch/x86/mm.c
>> @@ -4591,6 +4591,26 @@ int xenmem_add_to_physmap_one(
>> return rc;
>> }
>>
>> +unsigned int arch_resource_max_frames(
>> + struct domain *d, unsigned int type, unsigned int id)
>> +{
>> + unsigned int nr = 0;
>> +
>> + switch ( type )
>> + {
>> +#ifdef CONFIG_HVM
>> + case XENMEM_resource_ioreq_server:
>> + if ( !is_hvm_domain(d) )
>> + break;
>> + /* One frame for the buf-ioreq ring, and one frame per 128 vcpus. */
>> + nr = 1 + DIV_ROUND_UP(d->max_vcpus * sizeof(struct ioreq), PAGE_SIZE);
> The buf-ioreq ring is optional
Yes, but it's position within the resource, and effect on the position
of the ioreq page(s), is not.
> so a caller using this value may still get a resource acquisition failure unless the id is used to actually look up and check the ioreq server in question for the actual maximum.
Yes, but that is potentially true of *any* acquisition attempt, even if
the id matches, because maybe someone else has destroyed the ioreq
server, or the domain, in the meantime.
What we have is an mmap() where the caller needs to know to not try and
map page 0 for an ioreq server where buf-ioreq doesn't exist.
This is a direct consequence of:
#define XENMEM_resource_ioreq_server_frame_bufioreq 0
#define XENMEM_resource_ioreq_server_frame_ioreq(n) (1 + (n))
and in practice, what a qemu/demu/other needs to do to map just the
ioreq frames (in a manner compatible with >127 vcpu HVM domains) is to
query the resource size and map size-1 pages from offset 1.
~Andrew
next prev parent reply other threads:[~2020-09-24 10:58 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-22 18:24 [PATCH v2 00/11] Multiple fixes to XENMEM_acquire_resource Andrew Cooper
2020-09-22 18:24 ` [PATCH v2 01/11] xen/memory: Introduce CONFIG_ARCH_ACQUIRE_RESOURCE Andrew Cooper
2020-09-22 18:24 ` [PATCH v2 02/11] xen/gnttab: Rework resource acquisition Andrew Cooper
2020-09-24 9:51 ` Paul Durrant
2021-01-11 21:22 ` Andrew Cooper
2021-01-12 8:23 ` Jan Beulich
2021-01-12 20:06 ` Andrew Cooper
2021-01-12 8:29 ` Paul Durrant
2020-09-25 13:17 ` Jan Beulich
2021-01-11 21:22 ` Andrew Cooper
2021-01-12 8:15 ` Jan Beulich
2021-01-12 18:11 ` Andrew Cooper
2020-09-22 18:24 ` [PATCH v2 03/11] xen/memory: Fix compat XENMEM_acquire_resource for size requests Andrew Cooper
2020-09-22 18:24 ` [PATCH v2 04/11] xen/memory: Fix acquire_resource size semantics Andrew Cooper
2020-09-24 10:06 ` Paul Durrant
2020-09-24 10:57 ` Andrew Cooper [this message]
2020-09-24 11:04 ` Paul Durrant
2020-09-25 15:56 ` Jan Beulich
2020-09-22 18:24 ` [PATCH v2 05/11] tools/foreignmem: Support querying the size of a resource Andrew Cooper
2021-01-08 17:52 ` Andrew Cooper
2021-01-11 10:50 ` Roger Pau Monné
2021-01-11 15:00 ` Andrew Cooper
2021-01-11 15:26 ` [PATCH v3 " Andrew Cooper
2021-01-11 15:54 ` Roger Pau Monné
2020-09-22 18:24 ` [PATCH v2 06/11] xen/memory: Clarify the XENMEM_acquire_resource ABI description Andrew Cooper
2020-09-24 10:08 ` Paul Durrant
2020-09-22 18:24 ` [PATCH v2 07/11] xen/memory: Improve compat XENMEM_acquire_resource handling Andrew Cooper
2020-09-24 10:16 ` Paul Durrant
2020-09-28 9:09 ` Jan Beulich
2021-01-08 18:57 ` Andrew Cooper
2021-01-11 14:25 ` Jan Beulich
2020-09-22 18:24 ` [PATCH v2 08/11] xen/memory: Indent part of acquire_resource() Andrew Cooper
2020-09-24 10:36 ` Paul Durrant
2020-09-22 18:24 ` [PATCH v2 09/11] xen/memory: Fix mapping grant tables with XENMEM_acquire_resource Andrew Cooper
2020-09-24 10:47 ` Paul Durrant
2021-01-08 19:36 ` Andrew Cooper
2020-09-28 9:37 ` Jan Beulich
2021-01-11 20:05 ` Andrew Cooper
2021-01-11 22:36 ` Andrew Cooper
2021-01-12 8:39 ` Jan Beulich
2020-09-22 18:24 ` [PATCH v2 10/11] TESTING dom0 Andrew Cooper
2020-09-22 18:24 ` [PATCH v2 11/11] TESTING XTF Andrew Cooper
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