On Wed, 2022-12-21 at 16:30 +0800, Yu Zhang wrote:
> On Fri, Dec 09, 2022 at 12:45:56PM +0800, Robert Hoo wrote:
> > When only changes LAM bits, ask next vcpu run to load mmu pgd, so
> > that it
> > will build new CR3 with LAM bits updates. No TLB flush needed on
> > this case.
> > When changes on effective addresses, no matter LAM bits changes or
> > not, go
> > through normal pgd update process.
>
> Sorry, may I ask why this is related to effective address changes?
> This patch is only about the CR3 updates...
>
Not sure if we mean the same thing. Here effective address I mean the
CR3 & CR3_ADDR_MASK, i.e. pgd part.
> >
> > Signed-off-by: Robert Hoo <robert.hu@xxxxxxxxxxxxxxx>
> > ---
> > arch/x86/kvm/x86.c | 24 ++++++++++++++++++++----
> > 1 file changed, 20 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 48a2ad1e4cd6..6fbe8dd36b1e 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -1248,9 +1248,9 @@ static bool kvm_is_valid_cr3(struct kvm_vcpu
> > *vcpu, unsigned long cr3)
> > int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
> > {
> > bool skip_tlb_flush = false;
> > - unsigned long pcid = 0;
> > + unsigned long pcid = 0, old_cr3;
> > #ifdef CONFIG_X86_64
> > - bool pcid_enabled = kvm_read_cr4_bits(vcpu, X86_CR4_PCIDE);
> > + bool pcid_enabled = !!kvm_read_cr4_bits(vcpu, X86_CR4_PCIDE);
>
> This may qualify a seperate patch. :)
I had thought of this as well, but it is so trivial, and literally we
cannot say original code is wrong.
>
> >
> > if (pcid_enabled) {
> > skip_tlb_flush = cr3 & X86_CR3_PCID_NOFLUSH;
> > @@ -1263,6 +1263,10 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu,
> > unsigned long cr3)
> > if (cr3 == kvm_read_cr3(vcpu) && !is_pae_paging(vcpu))
> > goto handle_tlb_flush;
> >
> > + if (!guest_cpuid_has(vcpu, X86_FEATURE_LAM) &&
> > + (cr3 & (X86_CR3_LAM_U48 | X86_CR3_LAM_U57)))
> > + return 1;
> > +
> > /*
> > * Do not condition the GPA check on long mode, this helper is
> > used to
> > * stuff CR3, e.g. for RSM emulation, and there is no guarantee
> > that
> > @@ -1274,8 +1278,20 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu,
> > unsigned long cr3)
> > if (is_pae_paging(vcpu) && !load_pdptrs(vcpu, cr3))
> > return 1;
> >
> > - if (cr3 != kvm_read_cr3(vcpu))
> > - kvm_mmu_new_pgd(vcpu, cr3);
> > + old_cr3 = kvm_read_cr3(vcpu);
> > + if (cr3 != old_cr3) {
> > + if ((cr3 ^ old_cr3) & CR3_ADDR_MASK) {
> > + kvm_mmu_new_pgd(vcpu, cr3 & ~(X86_CR3_LAM_U48 |
> > + X86_CR3_LAM_U57));
> > + } else {
> > + /*
> > + * Though effective addr no change, mark the
>
> Same question here.
Here is the case the CR3 updates are only of LAM bits, no changes to
PGD part.
>
> > + * request so that LAM bits will take effect
> > + * when enter guest.
> > + */
> > + kvm_make_request(KVM_REQ_LOAD_MMU_PGD, vcpu);
> > + }
> > + }
> >
> > vcpu->arch.cr3 = cr3;
> > kvm_register_mark_dirty(vcpu, VCPU_EXREG_CR3);
> > --
>
> B.R.
> Yu
