On 04/29/2010 02:22 AM, Marcelo Tosatti wrote:
On Wed, Apr 28, 2010 at 04:47:14PM +0300, Avi Kivity wrote:
Currently we run with EFER.NX=1 on the guest even if the guest value is 0.
This is fine with shadow, since we check bit 63 when instantiating a page
table, and fault if bit 63 is set while EFER.NX is clear.
This doesn't work with EPT, since we no longer get the change to check guest
ptes. So we need to run with EFER.NX=0.
This is complicated by the fact that if we switch EFER.NX on the host, we'll
trap immediately, since some host pages are mapped with the NX bit set. As
a result, we need to switch the MSR atomically during guest entry and exit.
Applied, thanks.
Out of curiosity, did you measure the vmentry/vmexit overhead?
Just did now.
nx=0: 3384
nx=1: 2203
Perhaps using the dedicated vmcs field is faster (but since it's
optional, we have to support the generic autoload area).
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
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