Re: [PATCH v6 6/6] KVM: VMX: Move VERW closer to VMentry for MDS mitigation

[Pawan Gupta <pawan.kumar.gupta@linux.intel.com>]

On Fri, Jan 26, 2024 at 01:31:54PM -0800, Sean Christopherson wrote:
> On Tue, Jan 23, 2024, Pawan Gupta wrote:
> > During VMentry VERW is executed to mitigate MDS. After VERW, any memory
> > access like register push onto stack may put host data in MDS affected
> > CPU buffers. A guest can then use MDS to sample host data.
> > 
> > Although likelihood of secrets surviving in registers at current VERW
> > callsite is less, but it can't be ruled out. Harden the MDS mitigation
> > by moving the VERW mitigation late in VMentry path.
> > 
> > Note that VERW for MMIO Stale Data mitigation is unchanged because of
> > the complexity of per-guest conditional VERW which is not easy to handle
> > that late in asm with no GPRs available. If the CPU is also affected by
> > MDS, VERW is unconditionally executed late in asm regardless of guest
> > having MMIO access.
> > 
> > Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
> > ---
> 
> Acked-by: Sean Christopherson <seanjc@google.com>

Thanks.