Re: [RFC PATCH v2 06/25] KVM: SVM: Fallback to flush everything if FLUSHBYASID is not available

[Sean Christopherson]

On Tue, Jun 16, 2026, Yosry Ahmed wrote:
> Currently, if FLUSHBYASID is not available when performing a TLB flush,
> the fallback is decrementing the ASID generation to trigger allocating a
> new ASID. In preparation for using a static ASID per vCPU (like VMX),
> just fallback to flushing everything if FLUSHBYASID is not available.
> This is probably worse from a performance perspective, but FLUSHBYASID
> has been around for ~15 years and it's not worth carrying the
> complexity.
> 
> The fallback logic is moved within vmcb_set_flush_asid(), as more

Phrase this as a command, not a description, i.e. "Move the fallback logic into
blah blah blah...".

> callers will be added and will need the fallback as well. The only other
> current caller is from SEV code, and no CPUs support SEV but not
> FLUSHBYASID (at least according to AI).