linux-kernel - Re: [PATCH v3 00/12] KVM: Add host swap event notifications for PV guest

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: <20100108161828.GA30404@amt.cnet>
Date:	Fri, 8 Jan 2010 14:18:28 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	kvm@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, avi@...hat.com, mingo@...e.hu,
	a.p.zijlstra@...llo.nl, tglx@...utronix.de, hpa@...or.com,
	riel@...hat.com, cl@...ux-foundation.org
Subject: Re: [PATCH v3 00/12] KVM: Add host swap event notifications for PV
	guest

On Tue, Jan 05, 2010 at 04:12:42PM +0200, Gleb Natapov wrote:
> KVM virtualizes guest memory by means of shadow pages or HW assistance
> like NPT/EPT. Not all memory used by a guest is mapped into the guest
> address space or even present in a host memory at any given time.
> When vcpu tries to access memory page that is not mapped into the guest
> address space KVM is notified about it. KVM maps the page into the guest
> address space and resumes vcpu execution. If the page is swapped out
> from host memory vcpu execution is suspended till the page is not swapped
> into the memory again. This is inefficient since vcpu can do other work
> (run other task or serve interrupts) while page gets swapped in.
> 
> To overcome this inefficiency this patch series implements "asynchronous
> page fault" for paravirtualized KVM guests. If a page that vcpu is
> trying to access is swapped out KVM sends an async PF to the vcpu
> and continues vcpu execution. Requested page is swapped in by another
> thread in parallel.  When vcpu gets async PF it puts faulted task to
> sleep until "wake up" interrupt is delivered. When the page is brought
> to the host memory KVM sends "wake up" interrupt and the guest's task
> resumes execution.

Some high level comments:

- cr2 used as token: better use the shared region? what if:
 
 async pf queued
 guest triple faults without a vmexit
 inject async-pf-done with token in cr2

Also, in such scenario, can't you potentially corrupt guest memory after
the triple fault by writing to the previously registered shared region
address?

- The token can overflow relatively easy. Use u64?

- Does it really inject interrupts for non-pv guests while waiting
for swapin? Can't see that. Wish it was more geared towards fv.

- Please share some perf numbers.

- Limit the number of queued async pf's per guest ?

- Unify gfn_to_pfn / gfn_to_pfn_async code in the pf handlers (easier
to review).

--
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/