Re: [PATCH v19 060/130] KVM: x86/tdp_mmu: Apply mmu notifier callback to only shared GPA

Binbin Wu
2024-03-28T08:29:55Z

On 2/26/2024 4:26 PM, isaku.yamahata@intel.com wrote:
> From: Isaku Yamahata <isaku.yamahata@intel.com>
>
> The private GPAs that typically guest memfd backs aren't subject to MMU
> notifier because it isn't mapped into virtual address of user process.
> kvm_tdp_mmu_handle_gfn() handles the callback of the MMU notifier,
> clear_flush_young(), clear_young(), test_young()() and change_pte(). Make
^
an extra "()"
> kvm_tdp_mmu_handle_gfn() aware of private mapping and skip private mapping.
>
> Even with AS_UNMOVABLE set, those mmu notifier are called. For example,
> ksmd triggers change_pte().

The description about the "AS_UNMOVABLE", you are refering to shared
memory, right?
Then, it seems not related to the change of this patch.

>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
> ---
> v19:
> - type: test_gfn() => test_young()
>
> v18:
> - newly added
>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> ---
> arch/x86/kvm/mmu/tdp_mmu.c | 22 +++++++++++++++++++++-
> 1 file changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index e7514a807134..10507920f36b 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -1157,9 +1157,29 @@ static __always_inline bool kvm_tdp_mmu_handle_gfn(struct kvm *kvm,
> * into this helper allow blocking; it'd be dead, wasteful code.
> */
> for_each_tdp_mmu_root(kvm, root, range->slot->as_id) {
> + gfn_t start, end;
> +
> + /*
> + * This function is called on behalf of mmu_notifier of
> + * clear_flush_young(), clear_young(), test_young()(), and

^
an extra
"()""

> + * change_pte(). They apply to only shared GPAs.
> + */
> + WARN_ON_ONCE(range->only_private);
> + WARN_ON_ONCE(!range->only_shared);
> + if (is_private_sp(root))
> + continue;
> +
> + /*
> + * For TDX shared mapping, set GFN shared bit to the range,
> + * so the handler() doesn't need to set it, to avoid duplicated
> + * code in multiple handler()s.
> + */
> + start = kvm_gfn_to_shared(kvm, range->start);
> + end = kvm_gfn_to_shared(kvm, range->end);
> +
> rcu_read_lock();
>
> - tdp_root_for_each_leaf_pte(iter, root, range->start, range->end)
> + tdp_root_for_each_leaf_pte(iter, root, start, end)
> ret |= handler(kvm, &iter, range);
>
> rcu_read_unlock();