linux-kernel - Re: [Qemu-devel] [RFC] Next gen kvm api

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: <4F3BB41E.60405@redhat.com>
Date:	Wed, 15 Feb 2012 15:33:18 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Anthony Liguori <anthony@...emonkey.ws>
CC:	Alexander Graf <agraf@...e.de>, qemu-devel <qemu-devel@...gnu.org>,
	kvm-ppc <kvm-ppc@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [Qemu-devel] [RFC] Next gen kvm api

On 02/07/2012 05:23 PM, Anthony Liguori wrote:
> On 02/07/2012 07:40 AM, Alexander Graf wrote:
>>
>> Why? For the HPET timer register for example, we could have a simple
>> MMIO hook that says
>>
>>    on_read:
>>      return read_current_time() - shared_page.offset;
>>    on_write:
>>      handle_in_user_space();
>>
>> For IDE, it would be as simple as
>>
>>    register_pio_hook_ptr_r(PIO_IDE, SIZE_BYTE,&s->cmd[0]);
>>    for (i = 1; i<  7; i++) {
>>      register_pio_hook_ptr_r(PIO_IDE + i, SIZE_BYTE,&s->cmd[i]);
>>      register_pio_hook_ptr_w(PIO_IDE + i, SIZE_BYTE,&s->cmd[i]);
>>    }
>
> You can't easily serialize updates to that address with the kernel
> since two threads are likely going to be accessing it at the same
> time.  That either means an expensive sync operation or a reliance on
> atomic instructions.
>
> But not all architectures offer non-word sized atomic instructions so
> it gets fairly nasty in practice.
>

I doubt that any guest accesses IDE registers from two threads in
parallel.  The guest will have some lock, so we could have a lock as
well and be assured that there will never be contention.

-- 
error compiling committee.c: too many arguments to function

--
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/