From: "Huang, Kai" <kai.huang@intel.com>
To: Isaku Yamahata <isaku.yamahata@linux.intel.com>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"Yamahata, Isaku" <isaku.yamahata@intel.com>,
"federico.parola@polito.it" <federico.parola@polito.it>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"dmatlack@google.com" <dmatlack@google.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"isaku.yamahata@gmail.com" <isaku.yamahata@gmail.com>,
"michael.roth@amd.com" <michael.roth@amd.com>,
"seanjc@google.com" <seanjc@google.com>
Subject: Re: [RFC PATCH 1/8] KVM: Document KVM_MAP_MEMORY ioctl
Date: Fri, 8 Mar 2024 13:20:55 +1300 [thread overview]
Message-ID: <35141245-ce1a-4315-8597-3df4f66168f8@intel.com> (raw)
In-Reply-To: <20240307203340.GI368614@ls.amr.corp.intel.com>
>>>
>>> +4.143 KVM_MAP_MEMORY
>>> +------------------------
>>> +
>>> +:Capability: KVM_CAP_MAP_MEMORY
>>> +:Architectures: none
>>> +:Type: vcpu ioctl
>>
>> I think "vcpu ioctl" means theoretically it can be called on multiple vcpus.
>>
>> What happens in that case?
>
> Each vcpu can handle the ioctl simaltaneously.
Not sure whether it is implied, but should we document it can be called
simultaneously?
Also, I believe this is only supposed to be called before VM starts to
run? I think we should document that too.
This is userspace ABI, we need to be explicit on how it is supposed to
be called from userspace.
Btw, I believe there should be some justification in the changelog why
this should be a vcpu ioctl().
[...]
>>> +:Parameters: struct kvm_memory_mapping(in/out)
>>> +:Returns: 0 on success, <0 on error
>>> +
>>> +KVM_MAP_MEMORY populates guest memory without running vcpu.
>>> +
>>> +::
>>> +
>>> + struct kvm_memory_mapping {
>>> + __u64 base_gfn;
>>> + __u64 nr_pages;
>>> + __u64 flags;
>>> + __u64 source;
>>> + };
>>> +
>>> + /* For kvm_memory_mapping:: flags */
>>> + #define KVM_MEMORY_MAPPING_FLAG_WRITE _BITULL(0)
>>> + #define KVM_MEMORY_MAPPING_FLAG_EXEC _BITULL(1)
>>> + #define KVM_MEMORY_MAPPING_FLAG_USER _BITULL(2)
>>
>> I am not sure what's the good of having "FLAG_USER"?
>>
>> This ioctl is called from userspace, thus I think we can just treat this always
>> as user-fault?
>
> The point is how to emulate kvm page fault as if vcpu caused the kvm page
> fault. Not we call the ioctl as user context.
Sorry I don't quite follow. What's wrong if KVM just append the #PF
USER error bit before it calls into the fault handler?
My question is, since this is ABI, you have to tell how userspace is
supposed to use this. Maybe I am missing something, but I don't see how
USER should be used here.
next prev parent reply other threads:[~2024-03-08 0:21 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-01 17:28 [RFC PATCH 0/8] KVM: Prepopulate guest memory API isaku.yamahata
2024-03-01 17:28 ` [RFC PATCH 1/8] KVM: Document KVM_MAP_MEMORY ioctl isaku.yamahata
2024-03-07 0:43 ` David Matlack
2024-03-07 1:29 ` Isaku Yamahata
2024-03-07 12:30 ` Huang, Kai
2024-03-07 20:33 ` Isaku Yamahata
2024-03-08 0:20 ` Huang, Kai [this message]
2024-03-08 0:56 ` David Matlack
2024-03-08 1:28 ` Sean Christopherson
2024-03-08 2:19 ` Isaku Yamahata
2024-03-10 23:12 ` Michael Roth
2024-03-11 1:05 ` Huang, Kai
2024-03-11 1:08 ` Huang, Kai
2024-03-12 1:34 ` Isaku Yamahata
2024-03-01 17:28 ` [RFC PATCH 2/8] KVM: Add KVM_MAP_MEMORY vcpu ioctl to pre-populate guest memory isaku.yamahata
2024-03-07 0:49 ` David Matlack
2024-03-07 2:52 ` Isaku Yamahata
2024-03-07 12:45 ` Huang, Kai
2024-03-07 20:41 ` Isaku Yamahata
2024-03-11 17:23 ` Sean Christopherson
2024-03-11 22:19 ` Isaku Yamahata
2024-03-01 17:28 ` [RFC PATCH 3/8] KVM: x86/mmu: Introduce initialier macro for struct kvm_page_fault isaku.yamahata
2024-03-11 17:24 ` Sean Christopherson
2024-03-11 22:56 ` Isaku Yamahata
2024-03-01 17:28 ` [RFC PATCH 4/8] KVM: x86/mmu: Factor out kvm_mmu_do_page_fault() isaku.yamahata
2024-03-01 17:28 ` [RFC PATCH 5/8] KVM: x86/mmu: Introduce kvm_mmu_map_page() for prepopulating guest memory isaku.yamahata
2024-03-07 0:38 ` David Matlack
2024-03-19 15:53 ` Isaku Yamahata
2024-03-11 17:29 ` Sean Christopherson
2024-03-11 22:57 ` Isaku Yamahata
2024-03-01 17:28 ` [RFC PATCH 6/8] KVM: x86: Implement kvm_arch_{, pre_}vcpu_map_memory() isaku.yamahata
2024-03-07 0:30 ` David Matlack
2024-03-07 0:36 ` David Matlack
2024-03-07 1:51 ` Isaku Yamahata
2024-03-19 16:26 ` Isaku Yamahata
2024-04-03 23:15 ` Sean Christopherson
2024-03-07 1:34 ` Isaku Yamahata
2024-03-11 23:26 ` Sean Christopherson
2024-03-12 12:38 ` Huang, Kai
2024-03-12 14:20 ` Sean Christopherson
2024-03-12 21:41 ` Huang, Kai
2024-03-12 21:46 ` Huang, Kai
2024-03-12 23:03 ` Sean Christopherson
2024-03-01 17:28 ` [RFC PATCH 7/8] KVM: x86: Add hooks in kvm_arch_vcpu_map_memory() isaku.yamahata
2024-03-01 17:28 ` [RFC PATCH 8/8] KVM: selftests: x86: Add test for KVM_MAP_MEMORY isaku.yamahata
2024-03-07 0:53 ` [RFC PATCH 0/8] KVM: Prepopulate guest memory API David Matlack
2024-03-07 2:09 ` Isaku Yamahata
2024-03-19 16:33 ` Isaku Yamahata
2024-04-03 18:30 ` Sean Christopherson
2024-04-03 22:00 ` Isaku Yamahata
2024-04-03 22:42 ` Sean Christopherson
2024-03-11 3:20 ` Michael Roth
2024-03-11 23:44 ` Sean Christopherson
2024-03-12 1:32 ` Isaku Yamahata
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