From: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
To: Avi Kivity <avi@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
LKML <linux-kernel@vger.kernel.org>, KVM <kvm@vger.kernel.org>
Subject: Re: [PATCH v6 01/12] KVM: x86: fix possible infinite loop caused by reexecute_instruction
Date: Wed, 22 Aug 2012 20:49:26 +0800 [thread overview]
Message-ID: <5034D556.1080804@linux.vnet.ibm.com> (raw)
In-Reply-To: <5034CA2D.30903@redhat.com>
On 08/22/2012 08:01 PM, Avi Kivity wrote:
> On 08/21/2012 05:57 AM, Xiao Guangrong wrote:
>> Currently, we reexecute all unhandleable instructions if they do not
>> access on the mmio, however, it can not work if host map the readonly
>> memory to guest. If the instruction try to write this kind of memory,
>> it will fault again when guest retry it, then we will goto a infinite
>> loop: retry instruction -> write #PF -> emulation fail ->
>> retry instruction -> ...
>>
>> Fix it by retrying the instruction only when it faults on the writable
>> memory
>>
>> Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
>> ---
>> arch/x86/kvm/x86.c | 12 +++++++++++-
>> 1 files changed, 11 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index fb0d937..704680d 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -4473,6 +4473,7 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu)
>> static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t gva)
>> {
>> gpa_t gpa;
>> + pfn_t pfn;
>>
>> if (tdp_enabled)
>> return false;
>> @@ -4490,8 +4491,17 @@ static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t gva)
>> if (gpa == UNMAPPED_GVA)
>> return true; /* let cpu generate fault */
>>
>> - if (!kvm_is_error_hva(gfn_to_hva(vcpu->kvm, gpa >> PAGE_SHIFT)))
>> + /*
>> + * Do not retry the unhandleable instruction if it faults on the
>> + * readonly host memory, otherwise it will goto a infinite loop:
>> + * retry instruction -> write #PF -> emulation fail -> retry
>> + * instruction -> ...
>> + */
>> + pfn = gfn_to_pfn(vcpu->kvm, gpa_to_gfn(gpa));
>> + if (!is_error_pfn(pfn)) {
>> + kvm_release_pfn_clean(pfn);
>> return true;
>> + }
>>
>> return false;
>> }
>>
>
> Good catch. Did this actually happen or did you find it by code inspection?
>
It did not happen in my test. Actually, it is reported by Marcelo.
next prev parent reply other threads:[~2012-08-22 12:49 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-21 2:57 [PATCH v6 00/12] KVM: introduce readonly memslot Xiao Guangrong
2012-08-21 2:57 ` [PATCH v6 01/12] KVM: x86: fix possible infinite loop caused by reexecute_instruction Xiao Guangrong
2012-08-22 12:01 ` Avi Kivity
2012-08-22 12:49 ` Xiao Guangrong [this message]
2012-08-21 2:58 ` [PATCH v6 02/12] KVM: fix missing check for memslot flags Xiao Guangrong
2012-08-21 2:58 ` [PATCH v6 03/12] KVM: hide KVM_MEMSLOT_INVALID from userspace Xiao Guangrong
2012-08-21 2:59 ` [PATCH v6 04/12] KVM: introduce gfn_to_pfn_memslot_atomic Xiao Guangrong
2012-08-21 2:59 ` [PATCH v6 05/12] KVM: introduce gfn_to_hva_read/kvm_read_hva/kvm_read_hva_atomic Xiao Guangrong
2012-08-21 3:00 ` [PATCH v6 06/12] KVM: reorganize hva_to_pfn Xiao Guangrong
2012-08-21 3:00 ` [PATCH v6 07/12] KVM: use 'writable' as a hint to map writable pfn Xiao Guangrong
2012-08-21 3:01 ` [PATCH v6 08/12] KVM: introduce KVM_PFN_ERR_RO_FAULT Xiao Guangrong
2012-08-21 3:01 ` [PATCH v6 09/12] KVM: introduce KVM_HVA_ERR_BAD Xiao Guangrong
2012-08-21 3:02 ` [PATCH v6 10/12] KVM: introduce KVM_HVA_ERR_RO_BAD Xiao Guangrong
2012-08-21 3:02 ` [PATCH v6 11/12] KVM: introduce readonly memslot Xiao Guangrong
2012-09-07 10:23 ` Jan Kiszka
2012-09-07 10:47 ` Xiao Guangrong
2012-09-07 11:14 ` Jan Kiszka
2012-09-09 13:42 ` Avi Kivity
2012-09-09 13:52 ` Jan Kiszka
2012-08-21 3:03 ` [PATCH v6 12/12] KVM: indicate readonly access fault Xiao Guangrong
2012-08-22 12:06 ` Avi Kivity
2012-08-22 12:47 ` Xiao Guangrong
2012-09-06 14:09 ` Avi Kivity
2012-09-07 9:56 ` Xiao Guangrong
2012-09-09 13:46 ` Avi Kivity
2012-09-10 22:31 ` Marcelo Tosatti
2012-09-11 9:18 ` Avi Kivity
2012-09-11 14:39 ` Marcelo Tosatti
2012-09-12 15:27 ` Marcelo Tosatti
2012-09-12 15:34 ` Avi Kivity
2012-09-12 15:44 ` Marcelo Tosatti
2012-09-12 15:55 ` Avi Kivity
2012-08-22 12:09 ` [PATCH v6 00/12] KVM: introduce readonly memslot Avi Kivity
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