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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 6/7] xen/arm: tlbflush: Rework TLB helpers
On Wed, 8 May 2019, Julien Grall wrote:
> All the TLBs helpers invalidate all the TLB entries are using the same
> pattern:
> DSB SY
> TLBI ...
> DSB SY
> ISB
>
> This pattern is following pattern recommended by the Arm Arm to ensure
> visibility of updates to translation tables (see K11.5.2 in ARM DDI
> 0487D.b).
>
> We have been a bit too eager in Xen and use system-wide DSBs when this
> can be limited to the inner-shareable domain.
>
> Furthermore, the first DSB can be restrict further to only store in the
> inner-shareable domain. This is because the DSB is here to ensure
> visibility of the update to translation table walks.
>
> Lastly, there are a lack of documentation in most of the TLBs helper.
>
> Rather than trying to update the helpers one by one, this patch
> introduce a per-arch macro to generate the TLB helpers. This will be
> easier to update the TLBs helper in the future and the documentation.
>
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> Reviewed-by: Andrii Anisov <andrii_anisov@xxxxxxxx>
>
> ---
> Changes in v2:
> - Update the reference to the Arm Arm to the latest spec
> - Add Andrii's reviewed-by
> ---
> xen/include/asm-arm/arm32/flushtlb.h | 73 ++++++++++++++--------------------
> xen/include/asm-arm/arm64/flushtlb.h | 76
> +++++++++++++++---------------------
> 2 files changed, 60 insertions(+), 89 deletions(-)
>
> diff --git a/xen/include/asm-arm/arm32/flushtlb.h
> b/xen/include/asm-arm/arm32/flushtlb.h
> index b629db61cb..9085e65011 100644
> --- a/xen/include/asm-arm/arm32/flushtlb.h
> +++ b/xen/include/asm-arm/arm32/flushtlb.h
> @@ -1,59 +1,44 @@
> #ifndef __ASM_ARM_ARM32_FLUSHTLB_H__
> #define __ASM_ARM_ARM32_FLUSHTLB_H__
>
> -/* Flush local TLBs, current VMID only */
> -static inline void flush_guest_tlb_local(void)
> -{
> - dsb(sy);
> -
> - WRITE_CP32((uint32_t) 0, TLBIALL);
> -
> - dsb(sy);
> - isb();
> +/*
> + * Every invalidation operation use the following patterns:
> + *
> + * DSB ISHST // Ensure prior page-tables updates have completed
> + * TLBI... // Invalidate the TLB
> + * DSB ISH // Ensure the TLB invalidation has completed
> + * ISB // See explanation below
> + *
> + * For Xen page-tables the ISB will discard any instructions fetched
> + * from the old mappings.
> + *
> + * For the Stage-2 page-tables the ISB ensures the completion of the DSB
> + * (and therefore the TLB invalidation) before continuing. So we know
> + * the TLBs cannot contain an entry for a mapping we may have removed.
> + */
> +#define TLB_HELPER(name, tlbop) \
> +static inline void name(void) \
> +{ \
> + dsb(ishst); \
> + WRITE_CP32(0, tlbop); \
> + dsb(ish); \
> + isb(); \
> }
>
Hi Julien,
I agree with what you are trying to achieve with this patch and I like
the idea of reducing code duplication. As I look at the code, I was
hoping to find a way to avoid introducing macros and use static inline
functions instead, but it doesn't look like it is possible for arm32.
There is no way to pass TLBIALLIS as a parameter to a function for
instance. It might be possible for arm64 as they are just strings, but at
that point it might be better to keep the code similar between arm32 and
arm64 having both of them as macros, instead of having one as macro and
the other as static inline.
Do you agree with me? Can you see any other ways to turn TLB_HELPER into
a static inline?
> -/* Flush inner shareable TLBs, current VMID only */
> -static inline void flush_guest_tlb(void)
> -{
> - dsb(sy);
> -
> - WRITE_CP32((uint32_t) 0, TLBIALLIS);
> +/* Flush local TLBs, current VMID only */
> +TLB_HELPER(flush_guest_tlb_local, TLBIALL);
>
> - dsb(sy);
> - isb();
> -}
> +/* Flush inner shareable TLBs, current VMID only */
> +TLB_HELPER(flush_guest_tlb, TLBIALLIS);
>
> /* Flush local TLBs, all VMIDs, non-hypervisor mode */
> -static inline void flush_all_guests_tlb_local(void)
> -{
> - dsb(sy);
> -
> - WRITE_CP32((uint32_t) 0, TLBIALLNSNH);
> -
> - dsb(sy);
> - isb();
> -}
> +TLB_HELPER(flush_all_guests_tlb_local, TLBIALLNSNH);
>
> /* Flush innershareable TLBs, all VMIDs, non-hypervisor mode */
> -static inline void flush_all_guests_tlb(void)
> -{
> - dsb(sy);
> -
> - WRITE_CP32((uint32_t) 0, TLBIALLNSNHIS);
> -
> - dsb(sy);
> - isb();
> -}
> +TLB_HELPER(flush_all_guests_tlb, TLBIALLNSNHIS);
>
> /* Flush all hypervisor mappings from the TLB of the local processor. */
> -static inline void flush_xen_tlb_local(void)
> -{
> - asm volatile("dsb;" /* Ensure preceding are visible */
> - CMD_CP32(TLBIALLH)
> - "dsb;" /* Ensure completion of the TLB flush */
> - "isb;"
> - : : : "memory");
> -}
> +TLB_HELPER(flush_xen_tlb_local, TLBIALLH);
>
> /* Flush TLB of local processor for address va. */
> static inline void __flush_xen_tlb_one_local(vaddr_t va)
> diff --git a/xen/include/asm-arm/arm64/flushtlb.h
> b/xen/include/asm-arm/arm64/flushtlb.h
> index 2fed34b2ec..ceec59542e 100644
> --- a/xen/include/asm-arm/arm64/flushtlb.h
> +++ b/xen/include/asm-arm/arm64/flushtlb.h
> @@ -1,60 +1,46 @@
> #ifndef __ASM_ARM_ARM64_FLUSHTLB_H__
> #define __ASM_ARM_ARM64_FLUSHTLB_H__
>
> -/* Flush local TLBs, current VMID only */
> -static inline void flush_guest_tlb_local(void)
> -{
> - asm volatile(
> - "dsb sy;"
> - "tlbi vmalls12e1;"
> - "dsb sy;"
> - "isb;"
> - : : : "memory");
> +/*
> + * Every invalidation operation use the following patterns:
> + *
> + * DSB ISHST // Ensure prior page-tables updates have completed
> + * TLBI... // Invalidate the TLB
> + * DSB ISH // Ensure the TLB invalidation has completed
> + * ISB // See explanation below
> + *
> + * For Xen page-tables the ISB will discard any instructions fetched
> + * from the old mappings.
> + *
> + * For the Stage-2 page-tables the ISB ensures the completion of the DSB
> + * (and therefore the TLB invalidation) before continuing. So we know
> + * the TLBs cannot contain an entry for a mapping we may have removed.
> + */
> +#define TLB_HELPER(name, tlbop) \
> +static inline void name(void) \
> +{ \
> + asm volatile( \
> + "dsb ishst;" \
> + "tlbi " # tlbop ";" \
> + "dsb ish;" \
> + "isb;" \
> + : : : "memory"); \
> }
>
> +/* Flush local TLBs, current VMID only. */
> +TLB_HELPER(flush_guest_tlb_local, vmalls12e1);
> +
> /* Flush innershareable TLBs, current VMID only */
> -static inline void flush_guest_tlb(void)
> -{
> - asm volatile(
> - "dsb sy;"
> - "tlbi vmalls12e1is;"
> - "dsb sy;"
> - "isb;"
> - : : : "memory");
> -}
> +TLB_HELPER(flush_guest_tlb, vmalls12e1is);
>
> /* Flush local TLBs, all VMIDs, non-hypervisor mode */
> -static inline void flush_all_guests_tlb_local(void)
> -{
> - asm volatile(
> - "dsb sy;"
> - "tlbi alle1;"
> - "dsb sy;"
> - "isb;"
> - : : : "memory");
> -}
> +TLB_HELPER(flush_all_guests_tlb_local, alle1);
>
> /* Flush innershareable TLBs, all VMIDs, non-hypervisor mode */
> -static inline void flush_all_guests_tlb(void)
> -{
> - asm volatile(
> - "dsb sy;"
> - "tlbi alle1is;"
> - "dsb sy;"
> - "isb;"
> - : : : "memory");
> -}
> +TLB_HELPER(flush_all_guests_tlb, alle1is);
>
> /* Flush all hypervisor mappings from the TLB of the local processor. */
> -static inline void flush_xen_tlb_local(void)
> -{
> - asm volatile (
> - "dsb sy;" /* Ensure visibility of PTE writes */
> - "tlbi alle2;" /* Flush hypervisor TLB */
> - "dsb sy;" /* Ensure completion of TLB flush */
> - "isb;"
> - : : : "memory");
> -}
> +TLB_HELPER(flush_xen_tlb_local, alle2);
>
> /* Flush TLB of local processor for address va. */
> static inline void __flush_xen_tlb_one_local(vaddr_t va)
> --
> 2.11.0
>
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