Re: [PATCH v2 2/6] KVM: x86/mmu: Fix wrong gfn range of tlb flushing in kvm_set_pte_rmapp()

[David Matlack <dmatlack@google.com>]

On Wed, Aug 24, 2022 at 05:29:19PM +0800, Hou Wenlong wrote:
> When the spte of hupe page is dropped in kvm_set_pte_rmapp(),
> the whole gfn range covered by the spte should be flushed.
> However, rmap_walk_init_level() doesn't align down the gfn
> for new level like tdp iterator does, then the gfn used in
> kvm_set_pte_rmapp() is not the base gfn of huge page. And
> the size of gfn range is wrong too for huge page. Use the
> base gfn of huge page and the size of huge page for
> flushing tlbs for huge page.
> 
> Fixes: c3134ce240eed ("KVM: Replace old tlb flush function with new one to flush a specified range.")
> Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index a3578abd8bbc..3bcff56df109 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -1438,7 +1438,8 @@ static bool kvm_set_pte_rmap(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
>  	}
>  
>  	if (need_flush && kvm_available_flush_tlb_with_range()) {
> -		kvm_flush_remote_tlbs_with_address(kvm, gfn, 1);
> +		kvm_flush_remote_tlbs_with_address(kvm, gfn & -KVM_PAGES_PER_HPAGE(level),

Rounding down the GFN to a huge page size is a common pattern throughout
KVM. Can you introduce a common way of doing this and clean up the other
call sites?

> +						   KVM_PAGES_PER_HPAGE(level));

This eventually gets converted to kvm_flush_remote_tlbs_gfn() in a later
patch; which is even more reason to introduce
kvm_flush_remote_tlbs_gfn() in the previous patch.

>  		return false;
>  	}
>  
> -- 
> 2.31.1
>