[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH v6 1/9] x86/xpti: avoid copying L4 page table contents when possible

>>> On 10.04.18 at 09:58, <jgross@xxxxxxxx> wrote:
> For mitigation of Meltdown the current L4 page table is copied to the
> cpu local root page table each time a 64 bit pv guest is entered.
> Copying can be avoided in cases where the guest L4 page table hasn't
> been modified while running the hypervisor, e.g. when handling
> interrupts or any hypercall not modifying the L4 page table or %cr3.
> So add a per-cpu flag indicating whether the copying should be
> performed and set that flag only when loading a new %cr3 or modifying
> the L4 page table.  This includes synchronization of the cpu local
> root page table with other cpus, so add a special synchronization flag
> for that case.
> A simple performance check (compiling the hypervisor via "make -j 4")
> in dom0 with 4 vcpus shows a significant improvement:
> - real time drops from 112 seconds to 103 seconds
> - system time drops from 142 seconds to 131 seconds
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

> ---
> V6:
> - correct an error from rebasing to staging in assembly part

I have to admit that without digging out v5 I can't spot the


Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.