| Message ID | 20220712030835.286052-1-kai.huang@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM, x86/mmu: Fix the comment around kvm_tdp_mmu_zap_leafs() | expand |
On Tue, Jul 12, 2022, Kai Huang wrote: > Now kvm_tdp_mmu_zap_leafs() only zaps leaf SPTEs but not any non-root > pages within that GFN range anymore, so the comment isn't right. > > Fixes: f47e5bbbc92f ("KVM: x86/mmu: Zap only TDP MMU leafs in zap range and mmu_notifier unmap") > Signed-off-by: Kai Huang <kai.huang@intel.com> > --- > arch/x86/kvm/mmu/tdp_mmu.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > index f3a430d64975..7692e6273462 100644 > --- a/arch/x86/kvm/mmu/tdp_mmu.c > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > @@ -969,10 +969,9 @@ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root, > } > > /* > - * Tears down the mappings for the range of gfns, [start, end), and frees the > - * non-root pages mapping GFNs strictly within that range. Returns true if > - * SPTEs have been cleared and a TLB flush is needed before releasing the > - * MMU lock. > + * Zap leafs SPTEs for the range of gfns, [start, end) for all roots. Returns > + * true if SPTEs have been cleared and a TLB flush is needed before releasing > + * the MMU lock. What about shifting the comment from tdp_mmu_zap_leafs() instead of duplicating it? tdp_mmu_zap_leafs() is static and kvm_tdp_mmu_zap_leafs() is the sole caller. And opportunistically tweak the blurb about SPTEs being cleared to (a) say "zapped" instead of "cleared" because "cleared" will be wrong if/when KVM sets SUPPRESS_VE, and (b) to clarify that a flush is needed if and only if a SPTE has been zapped since MMU lock was last acquired. E.g. /* * If can_yield is true, will release the MMU lock and reschedule if the * scheduler needs the CPU or there is contention on the MMU lock. If this * function cannot yield, it will not release the MMU lock or reschedule and * the caller must ensure it does not supply too large a GFN range, or the * operation can cause a soft lockup. */ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root, gfn_t start, gfn_t end, bool can_yield, bool flush) /* * Zap leafs SPTEs for the range of gfns, [start, end), for all roots. Returns * true if a TLB flush is needed before releasing the MMU lock, i.e. if one or * more SPTEs were zapped since the MMU lock was last acquired. */ bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, int as_id, gfn_t start, gfn_t end, bool can_yield, bool flush)
On Tue, 2022-07-12 at 17:47 +0000, Sean Christopherson wrote: > On Tue, Jul 12, 2022, Kai Huang wrote: > > Now kvm_tdp_mmu_zap_leafs() only zaps leaf SPTEs but not any non-root > > pages within that GFN range anymore, so the comment isn't right. > > > > Fixes: f47e5bbbc92f ("KVM: x86/mmu: Zap only TDP MMU leafs in zap range and mmu_notifier unmap") > > Signed-off-by: Kai Huang <kai.huang@intel.com> > > --- > > arch/x86/kvm/mmu/tdp_mmu.c | 7 +++---- > > 1 file changed, 3 insertions(+), 4 deletions(-) > > > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > > index f3a430d64975..7692e6273462 100644 > > --- a/arch/x86/kvm/mmu/tdp_mmu.c > > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > > @@ -969,10 +969,9 @@ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root, > > } > > > > /* > > - * Tears down the mappings for the range of gfns, [start, end), and frees the > > - * non-root pages mapping GFNs strictly within that range. Returns true if > > - * SPTEs have been cleared and a TLB flush is needed before releasing the > > - * MMU lock. > > + * Zap leafs SPTEs for the range of gfns, [start, end) for all roots. Returns > > + * true if SPTEs have been cleared and a TLB flush is needed before releasing > > + * the MMU lock. > > What about shifting the comment from tdp_mmu_zap_leafs() instead of duplicating it? > tdp_mmu_zap_leafs() is static and kvm_tdp_mmu_zap_leafs() is the sole caller. And > opportunistically tweak the blurb about SPTEs being cleared to (a) say "zapped" > instead of "cleared" because "cleared" will be wrong if/when KVM sets SUPPRESS_VE, > and (b) to clarify that a flush is needed if and only if a SPTE has been zapped > since MMU lock was last acquired. > > E.g. > > /* > * If can_yield is true, will release the MMU lock and reschedule if the > * scheduler needs the CPU or there is contention on the MMU lock. If this > * function cannot yield, it will not release the MMU lock or reschedule and > * the caller must ensure it does not supply too large a GFN range, or the > * operation can cause a soft lockup. > */ > static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root, > gfn_t start, gfn_t end, bool can_yield, bool flush) > > /* > * Zap leafs SPTEs for the range of gfns, [start, end), for all roots. Returns > * true if a TLB flush is needed before releasing the MMU lock, i.e. if one or > * more SPTEs were zapped since the MMU lock was last acquired. > */ > bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, int as_id, gfn_t start, gfn_t end, > bool can_yield, bool flush) Yes looks better. Will send out a new patch soon. Thanks.
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index f3a430d64975..7692e6273462 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -969,10 +969,9 @@ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root, } /* - * Tears down the mappings for the range of gfns, [start, end), and frees the - * non-root pages mapping GFNs strictly within that range. Returns true if - * SPTEs have been cleared and a TLB flush is needed before releasing the - * MMU lock. + * Zap leafs SPTEs for the range of gfns, [start, end) for all roots. Returns + * true if SPTEs have been cleared and a TLB flush is needed before releasing + * the MMU lock. */ bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, int as_id, gfn_t start, gfn_t end, bool can_yield, bool flush)
Now kvm_tdp_mmu_zap_leafs() only zaps leaf SPTEs but not any non-root pages within that GFN range anymore, so the comment isn't right. Fixes: f47e5bbbc92f ("KVM: x86/mmu: Zap only TDP MMU leafs in zap range and mmu_notifier unmap") Signed-off-by: Kai Huang <kai.huang@intel.com> --- arch/x86/kvm/mmu/tdp_mmu.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-)