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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH Linux v2 7/7] xen: Add new Xen pv-op pte_get_and_clear.
On 10/09/2026 9:31 pm, Kevin Lampis wrote:
> If Xen supports XENFEAT_mmu_pt_update_swap then for performance reasons
> call mmu_update with the new MMU_PT_UPDATE_SWAP flag instead of
> native_ptep_get_and_clear().
>
> Signed-off-by: Kevin Lampis <kevin.lampis@xxxxxxxxxx>
CC Juergen, the Xen maintainer in Linux. Keeping the whole patch intact.
> ---
> Changes in v2:
> - New patch
> ---
> arch/x86/include/asm/paravirt.h | 5 +++++
> arch/x86/include/asm/paravirt_types.h | 1 +
> arch/x86/include/asm/pgtable.h | 3 ++-
> arch/x86/kernel/paravirt.c | 1 +
> arch/x86/xen/mmu_pv.c | 15 +++++++++++++++
> include/xen/interface/features.h | 2 ++
> include/xen/interface/xen.h | 1 +
> 7 files changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> index 0591aa38fd85..0a3a286c46f0 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -373,6 +373,11 @@ static inline void set_pmd(pmd_t *pmdp, pmd_t pmd)
> PVOP_VCALL2(pv_ops, mmu.set_pmd, pmdp, native_pmd_val(pmd));
> }
>
> +static inline pte_t pte_get_and_clear(pte_t *ptep)
> +{
> + return (pte_t){PVOP_CALL1(pte_t, mmu.pte_get_and_clear, ptep)};
> +}
> +
> static inline pmd_t __pmd(pmdval_t val)
> {
> return (pmd_t) { PVOP_ALT_CALLEE1(pmdval_t, pv_ops, mmu.make_pmd, val,
> diff --git a/arch/x86/include/asm/paravirt_types.h
> b/arch/x86/include/asm/paravirt_types.h
> index b4c4a23e77a1..1bd4c19450b5 100644
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -135,6 +135,7 @@ struct pv_mmu_ops {
> /* Pagetable manipulation functions */
> void (*set_pte)(pte_t *ptep, pte_t pteval);
> void (*set_pmd)(pmd_t *pmdp, pmd_t pmdval);
> + pte_t (*pte_get_and_clear)(pte_t *ptep);
>
> pte_t (*ptep_modify_prot_start)(struct vm_area_struct *vma, unsigned
> long addr,
> pte_t *ptep);
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index ac295ca6c92f..b0d7d6520984 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -58,6 +58,7 @@ extern pmdval_t early_pmd_flags;
> #include <asm/paravirt.h>
> #else /* !CONFIG_PARAVIRT_XXL */
> #define set_pte(ptep, pte) native_set_pte(ptep, pte)
> +#define pte_get_and_clear(ptep) native_ptep_get_and_clear(ptep)
>
> #define set_pte_atomic(ptep, pte) \
> native_set_pte_atomic(ptep, pte)
> @@ -1243,7 +1244,7 @@ bool ptep_clear_flush_young(struct vm_area_struct *vma,
> static inline pte_t ptep_get_and_clear(struct mm_struct *mm, unsigned long
> addr,
> pte_t *ptep)
> {
> - pte_t pte = native_ptep_get_and_clear(ptep);
> ++ pte_t pte = pte_get_and_clear(ptep);
This looks like a typo, on a path you didn't compile.
> page_table_check_pte_clear(mm, addr, pte);
> return pte;
> }
> diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
> index 00b59d774389..58ecd12b10ee 100644
> --- a/arch/x86/kernel/paravirt.c
> +++ b/arch/x86/kernel/paravirt.c
> @@ -178,6 +178,7 @@ struct paravirt_patch_template pv_ops = {
>
> .mmu.set_pte = native_set_pte,
> .mmu.set_pmd = native_set_pmd,
> + .mmu.pte_get_and_clear = native_ptep_get_and_clear,
>
> .mmu.ptep_modify_prot_start = __ptep_modify_prot_start,
> .mmu.ptep_modify_prot_commit = __ptep_modify_prot_commit,
> diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
> index 820af6f0aa57..7ce2feab6434 100644
> --- a/arch/x86/xen/mmu_pv.c
> +++ b/arch/x86/xen/mmu_pv.c
> @@ -359,6 +359,15 @@ static void xen_set_pte(pte_t *ptep, pte_t pteval)
> __xen_set_pte(ptep, pteval);
> }
>
> +static pte_t xen_pte_get_and_clear(pte_t *ptep)
> +{
> + struct mmu_update u;
> + u.ptr = virt_to_machine(ptep).maddr | MMU_PT_UPDATE_SWAP;
> + u.val = pte_val_ma(native_make_pte(0));
> + HYPERVISOR_mmu_update(&u, 1, NULL, DOMID_SELF);
> + return native_make_pte(u.val);
> +}
This wants some reformatting, and blank lines for clarity.
struct mmu_update u = {
.ptr = virt_to_machine(ptep).maddr | MMU_PT_UPDATE_SWAP,
.val = pte_val_ma(native_make_pte(0));
};
BUG_ON(HYPERVISOR_mmu_update(&u, 1, NULL, DOMID_SELF) != 1);
return native_make_pte(u.val);
I'm not a fan of the BUG_ON() error handling like this, but there really
is no other safe option in this case.
> +
> static pte_t xen_ptep_modify_prot_start(struct vm_area_struct *vma,
> unsigned long addr, pte_t *ptep)
> {
> @@ -2165,6 +2174,12 @@ static void __init xen_post_allocator_init(void)
> pv_ops.mmu.set_pud = xen_set_pud;
> pv_ops.mmu.set_p4d = xen_set_p4d;
>
> + if (xen_feature(XENFEAT_mmu_pt_update_swap))
> + pv_ops.mmu.pte_get_and_clear = xen_pte_get_and_clear;
> + else
> + pv_ops.mmu.pte_get_and_clear = native_ptep_get_and_clear;
> +
> +
Stray blank line.
~Andrew
> /* This will work as long as patching hasn't happened yet
> (which it hasn't) */
> pv_ops.mmu.alloc_pte = xen_alloc_pte;
> diff --git a/include/xen/interface/features.h
> b/include/xen/interface/features.h
> index 53f760378e39..b346d58c0a41 100644
> --- a/include/xen/interface/features.h
> +++ b/include/xen/interface/features.h
> @@ -97,6 +97,8 @@
> #define XENFEAT_not_direct_mapped 16
> #define XENFEAT_direct_mapped 17
>
> +#define XENFEAT_mmu_pt_update_swap 21
> +
> #define XENFEAT_NR_SUBMAPS 1
>
> #endif /* __XEN_PUBLIC_FEATURES_H__ */
> diff --git a/include/xen/interface/xen.h b/include/xen/interface/xen.h
> index 40c9793e9880..92f972e53323 100644
> --- a/include/xen/interface/xen.h
> +++ b/include/xen/interface/xen.h
> @@ -252,6 +252,7 @@
> #define MMU_MACHPHYS_UPDATE 1 /* ptr = MA of frame to modify entry
> for */
> #define MMU_PT_UPDATE_PRESERVE_AD 2 /* atomically: *ptr = val |
> (*ptr&(A|D)) */
> #define MMU_PT_UPDATE_NO_TRANSLATE 3 /* checked '*ptr = val'. ptr is MA.
> */
> +#define MMU_PT_UPDATE_SWAP 4
>
> /*
> * MMU EXTENDED OPERATIONS
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