On 16/04/2024 10:48 am, Yamahata, Isaku wrote:
On Mon, Apr 15, 2024 at 06:49:35AM -0700,
Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
On Fri, Apr 12, 2024, Isaku Yamahata wrote:
On Fri, Apr 12, 2024 at 03:46:05PM -0700,
Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
On Fri, Apr 12, 2024, Isaku Yamahata wrote:
On Fri, Apr 12, 2024 at 09:15:29AM -0700, Reinette Chatre <reinette.chatre@xxxxxxxxx> wrote:
+void tdx_mmu_release_hkid(struct kvm *kvm)
+{
+ while (__tdx_mmu_release_hkid(kvm) == -EBUSY)
+ ;
}
As I understand, __tdx_mmu_release_hkid() returns -EBUSY
after TDH.VP.FLUSH has been sent for every vCPU followed by
TDH.MNG.VPFLUSHDONE, which returns TDX_FLUSHVP_NOT_DONE.
Considering earlier comment that a retry of TDH.VP.FLUSH is not
needed, why is this while() loop here that sends the
TDH.VP.FLUSH again to all vCPUs instead of just a loop within
__tdx_mmu_release_hkid() to _just_ resend TDH.MNG.VPFLUSHDONE?
Could it be possible for a vCPU to appear during this time, thus
be missed in one TDH.VP.FLUSH cycle, to require a new cycle of
TDH.VP.FLUSH?
Yes. There is a race between closing KVM vCPU fd and MMU notifier release hook.
When KVM vCPU fd is closed, vCPU context can be loaded again.
But why is _loading_ a vCPU context problematic?
It's nothing problematic. It becomes a bit harder to understand why
tdx_mmu_release_hkid() issues IPI on each loop. I think it's reasonable
to make the normal path easy and to complicate/penalize the destruction path.
Probably I should've added comment on the function.
By "problematic", I meant, why can that result in a "missed in one TDH.VP.FLUSH
cycle"? AFAICT, loading a vCPU shouldn't cause that vCPU to be associated from
the TDX module's perspective, and thus shouldn't trigger TDX_FLUSHVP_NOT_DONE.
I.e. looping should be unnecessary, no?
The loop is unnecessary with the current code.
The possible future optimization is to reduce destruction time of Secure-EPT
somehow. One possible option is to release HKID while vCPUs are still alive and
destruct Secure-EPT with multiple vCPU context. Because that's future
optimization, we can ignore it at this phase.
I kinda lost here.
I thought in the current v19 code, you have already implemented this
optimization?
Or is this optimization totally different from what we discussed in an
earlier patch?
https://lore.kernel.org/lkml/8feaba8f8ef249950b629f3a8300ddfb4fbcf11c.camel@xxxxxxxxx/
