linux-kernel - Re: [PATCH v2 2/6] LoongArch: KVM: Select huge page only if secondary mmu supports it

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Message-ID: <CAAhV-H7YXHwfdy-DFAd6_qPXdqbBVUSHq0U8Hu1eEgdtN_b+OA@mail.gmail.com>
Date: Sun, 23 Jun 2024 15:55:42 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Bibo Mao <maobibo@...ngson.cn>
Cc: Tianrui Zhao <zhaotianrui@...ngson.cn>, WANG Xuerui <kernel@...0n.name>, 
	Sean Christopherson <seanjc@...gle.com>, kvm@...r.kernel.org, loongarch@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/6] LoongArch: KVM: Select huge page only if secondary
 mmu supports it

Hi, Bibo,

On Wed, Jun 19, 2024 at 4:09 PM Bibo Mao <maobibo@...ngson.cn> wrote:
>
> Currently page level selection about secondary mmu depends on memory
> slot and page level about host mmu. There will be problem if page level
> of secondary mmu is zero already. So page level selection should depend
> on the following three conditions.
>  1. Memslot is aligned for huge page and vm is not migrating.
>  2. Page level of host mmu is huge page also.
>  3. Page level of secondary mmu is suituable for huge page, it cannot
> be normal page since it is not supported to merge normal pages into
> huge page now.
>
> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> ---
>  arch/loongarch/include/asm/kvm_mmu.h |  2 +-
>  arch/loongarch/kvm/mmu.c             | 16 +++++++++++++---
>  2 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/kvm_mmu.h b/arch/loongarch/include/asm/kvm_mmu.h
> index 099bafc6f797..d06ae0e0dde5 100644
> --- a/arch/loongarch/include/asm/kvm_mmu.h
> +++ b/arch/loongarch/include/asm/kvm_mmu.h
> @@ -55,7 +55,7 @@ static inline void kvm_set_pte(kvm_pte_t *ptep, kvm_pte_t val)
>  static inline int kvm_pte_write(kvm_pte_t pte) { return pte & _PAGE_WRITE; }
>  static inline int kvm_pte_dirty(kvm_pte_t pte) { return pte & _PAGE_DIRTY; }
>  static inline int kvm_pte_young(kvm_pte_t pte) { return pte & _PAGE_ACCESSED; }
> -static inline int kvm_pte_huge(kvm_pte_t pte) { return pte & _PAGE_HUGE; }
> +static inline int kvm_pte_huge(kvm_pte_t pte)  { return !!(pte & _PAGE_HUGE); }
Why do we need this change?

Huacai

>
>  static inline kvm_pte_t kvm_pte_mkyoung(kvm_pte_t pte)
>  {
> diff --git a/arch/loongarch/kvm/mmu.c b/arch/loongarch/kvm/mmu.c
> index 9e39d28fec35..c6351d13ca1b 100644
> --- a/arch/loongarch/kvm/mmu.c
> +++ b/arch/loongarch/kvm/mmu.c
> @@ -858,10 +858,20 @@ static int kvm_map_page(struct kvm_vcpu *vcpu, unsigned long gpa, bool write)
>
>         /* Disable dirty logging on HugePages */
>         level = 0;
> -       if (!fault_supports_huge_mapping(memslot, hva, write)) {
> -               level = 0;
> -       } else {
> +       if (fault_supports_huge_mapping(memslot, hva, write)) {
> +               /* Check page level about host mmu*/
>                 level = host_pfn_mapping_level(kvm, gfn, memslot);
> +               if (level == 1) {
> +                       /*
> +                        * Check page level about secondary mmu
> +                        * Disable hugepage if it is normal page on
> +                        * secondary mmu already
> +                        */
> +                       ptep = kvm_populate_gpa(kvm, NULL, gpa, 0);
> +                       if (ptep && !kvm_pte_huge(*ptep))
> +                               level = 0;
> +               }
> +
>                 if (level == 1) {
>                         gfn = gfn & ~(PTRS_PER_PTE - 1);
>                         pfn = pfn & ~(PTRS_PER_PTE - 1);
> --
> 2.39.3
>