On 02/03/2011 02:57 PM, Nadav Har'El wrote:
On Sun, Jan 30, 2011, Avi Kivity wrote about "Re: [PATCH 07/29] nVMX: Hold a vmcs02 for each vmcs12":
>..
> >+static int nested_create_current_vmcs(struct kvm_vcpu *vcpu)
> >+{
>...
> >+ if (vmx->nested.vmcs02_num>= NESTED_MAX_VMCS)
> >+ return -ENOMEM;
>
> I asked to replace this by dropping the entire vmcs02_list (or perhaps
> just its tail).
Hi, here is a completely rewritten patch.
Now we make no guarantee to keep one vmcs02 for each vmcs12. Rather, we
have a limited pool of vmcs02. If we can find the same vmcs02 that we
previously used for the current vmcs12. Otherwise, we can take any of them
(we take the least recently used) and just use that. Of course, if the
pool is not yet fool, we can also allocate a new vmcs02.
The current default size for the pool is 1, meaning that we just keep one
vmcs02 (per vcpu) for use in any L2, potentially many of them. Because in
this version prepare_vmcs02 each time sets all vmcs02 fields, and doesn't
try to avoid setting rarely modified fields, there's nothing to gain by
trying to start from the previous vmcs02 used to run a certain L2.
In the future, when we do have an optimized prepare_vmcs02 which doesn't
set every field each time, it will make sense to increase the pool size.
Subject: [PATCH 07/29] nVMX: Introduce vmcs02: VMCS used to run L2
We saw in a previous patch that L1 controls its L2 guest with a vcms12.
L0 needs to create a real VMCS for running L2. We call that "vmcs02".
A later patch will contain the code, prepare_vmcs02(), for filling the vmcs02
fields. This patch only contains code for allocating vmcs02.
In this version, prepare_vmcs02() sets *all* of vmcs02's fields each time we
enter from L1 to L2, so keeping just one vmcs02 for the vcpu would have
sufficed: It could be reused even when L1 runs multiple L2 guests.
However, in future versions we'll probably want to add an optimization where
vmcs02 fields that rarely change will not be set each time. For that reason
it is beneficial to keep around several vmcs02s of L2 guests that have
recently run, so that potentially we could run these L2s again more quickly
because less vmwrites to vmcs02 will be needed.
This patch adds to each vcpu a vmcs02 pool, vmx->nested.vmcs02_pool,
which remembers the vmcs02s last used to run up to VMCS02_POOL_SIZE L2s.
Because in the current version prepare_vmcs02() sets all vmcs02 fields no
matter what we start with, we choose VMCS02_POOL_SIZE=1. I.e., one vmcs02
is allocated (and loaded onto the processor), and it is reused to enter any
L2 guest. In the future, when prepare_vmcs02() is optimized not to set all
fields every time, VMCS02_POOL_SIZE should be increased.
Thanks, that looks much nicer.
--
error compiling committee.c: too many arguments to function
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