KVM: x86: Always load PDPTRs on CR3 load for SVM w/o NPT and a PAE guest

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Kill off pdptrs_changed() and instead go through the full kvm_set_cr3()
for PAE guest, even if the new CR3 is the same as the current CR3.  For
VMX, and SVM with NPT enabled, the PDPTRs are unconditionally marked as
unavailable after VM-Exit, i.e. the optimization is dead code except for
SVM without NPT.

In the unlikely scenario that anyone cares about SVM without NPT _and_ a
PAE guest, they've got bigger problems if their guest is loading the same
CR3 so frequently that the performance of kvm_set_cr3() is notable,
especially since KVM's fast PGD switching means reloading the same CR3
does not require a full rebuild.  Given that PAE and PCID are mutually
exclusive, i.e. a sync and flush are guaranteed in any case, the actual
benefits of the pdptrs_changed() optimization are marginal at best.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210607090203.133058-4-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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Sean Christopherson 2021-06-07 12:01:58 +03:00 • committed by Paolo Bonzini

parent a36dbec67e

commit c7313155bf

2 changed files with 2 additions and 33 deletions

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1

arch/x86/include/asm/kvm_host.h

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34

arch/x86/kvm/x86.c

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