On Mon, Jun 04, 2012 at 10:37:24AM +0530, Nikunj A. Dadhania wrote:
> flush_tlb_others_ipi depends on lot of statics in tlb.c. Replicated
> the flush_tlb_others_ipi as kvm_flush_tlb_others to further adapt to
> paravirtualization.
>
> Use the vcpu state information inside the kvm_flush_tlb_others to
> avoid sending ipi to pre-empted vcpus.
>
> * Do not send ipi's to offline vcpus and set flush_on_enter flag
> * For online vcpus: Wait for them to clear the flag
>
> The approach was discussed here: https://lkml.org/lkml/2012/2/20/157
>
> Suggested-by: Peter Zijlstra <[email protected]>
> Signed-off-by: Nikunj A. Dadhania <[email protected]>
Why not reintroduce the hypercall to flush TLBs? No waiting, no
entry/exit trickery.
This is half-way-there paravirt with all the downsides. Even though the
guest running information might be useful in other cases.
> Pseudo Algo:
>
> Write()
> ======
>
> guest_exit()
> flush_on_enter[i]=0;
> running[i] = 0;
>
> guest_enter()
> running[i] = 1;
> smp_mb();
> if(flush_on_enter[i]) {
> tlb_flush()
> flush_on_enter[i]=0;
> }
>
>
> Read()
> ======
>
> GUEST KVM-HV
>
> f->flushcpumask = cpumask - me;
>
> again:
> for_each_cpu(i, f->flushmask) {
>
> if (!running[i]) {
> case 1:
>
> running[n]=1
>
> (cpuN does not see
> flush_on_enter set,
> guest later finds it
> running and sends ipi,
> we are fine here, need
> to clear the flag on
> guest_exit)
>
> flush_on_enter[i] = 1;
> case2:
>
> running[n]=1
> (cpuN - will see flush
> on enter and an IPI as
> well - addressed in patch-4)
>
> if (!running[i])
> cpu_clear(f->flushmask); All is well, vm_enter
> will do the fixup
> }
> case 3:
> running[n] = 0;
>
> (cpuN went to sleep,
> we saw it as awake,
> ipi sent, but wait
> will break without
> zero_mask and goto
> again will take care)
>
> }
> send_ipi(f->flushmask)
>
> wait_a_while_for_zero_mask();
>
> if (!zero_mask)
> goto again;
> ---
> arch/x86/include/asm/kvm_para.h | 3 +-
> arch/x86/include/asm/tlbflush.h | 9 ++++++
> arch/x86/kernel/kvm.c | 1 +
> arch/x86/kvm/x86.c | 14 ++++++++-
> arch/x86/mm/tlb.c | 61
> +++++++++++++++++++++++++++++++++++++++
> 5 files changed, 86 insertions(+), 2 deletions(-)
>
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