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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH 21/22] xen/arm64: Implement a mapcache for arm64
On Fri, 16 Dec 2022, Julien Grall wrote:
> From: Julien Grall <jgrall@xxxxxxxxxx>
>
> At the moment, on arm64, map_domain_page() is implemented using
> virt_to_mfn(). Therefore it is relying on the directmap.
>
> In a follow-up patch, we will allow the admin to remove the directmap.
> Therefore we want to implement a mapcache.
>
> Thanksfully there is already one for arm32. So select ARCH_ARM_DOMAIN_PAGE
> and add the necessary boiler plate to support 64-bit:
> - The page-table start at level 0, so we need to allocate the level
> 1 page-table
> - map_domain_page() should check if the page is in the directmap. If
> yes, then use virt_to_mfn() to limit the performance impact
> when the directmap is still enabled (this will be selectable
> on the command line).
>
> Take the opportunity to replace first_table_offset(...) with offsets[...].
>
> Note that, so far, arch_mfns_in_directmap() always return true on
> arm64. So the mapcache is not yet used. This will change in a
> follow-up patch.
>
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> ----
>
> There are a few TODOs:
> - It is becoming more critical to fix the mapcache
> implementation (this is not compliant with the Arm Arm)
> - Evaluate the performance
> ---
> xen/arch/arm/Kconfig | 1 +
> xen/arch/arm/domain_page.c | 47 +++++++++++++++++++++++++++----
> xen/arch/arm/include/asm/config.h | 7 +++++
> xen/arch/arm/include/asm/mm.h | 5 ++++
> xen/arch/arm/mm.c | 6 ++--
> xen/arch/arm/setup.c | 4 +++
> 6 files changed, 62 insertions(+), 8 deletions(-)
>
> diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> index 239d3aed3c7f..9c58b2d5c3aa 100644
> --- a/xen/arch/arm/Kconfig
> +++ b/xen/arch/arm/Kconfig
> @@ -9,6 +9,7 @@ config ARM_64
> select 64BIT
> select ARM_EFI
> select HAS_FAST_MULTIPLY
> + select ARCH_MAP_DOMAIN_PAGE
>
> config ARM
> def_bool y
> diff --git a/xen/arch/arm/domain_page.c b/xen/arch/arm/domain_page.c
> index 4540b3c5f24c..f3547dc853ef 100644
> --- a/xen/arch/arm/domain_page.c
> +++ b/xen/arch/arm/domain_page.c
> @@ -1,4 +1,5 @@
> /* SPDX-License-Identifier: GPL-2.0-or-later */
> +#include <xen/domain_page.h>
> #include <xen/mm.h>
> #include <xen/pmap.h>
> #include <xen/vmap.h>
> @@ -8,6 +9,8 @@
> /* Override macros from asm/page.h to make them work with mfn_t */
> #undef virt_to_mfn
> #define virt_to_mfn(va) _mfn(__virt_to_mfn(va))
> +#undef mfn_to_virt
> +#define mfn_to_virt(va) __mfn_to_virt(mfn_x(mfn))
>
> /* cpu0's domheap page tables */
> static DEFINE_PAGE_TABLES(cpu0_dommap, DOMHEAP_SECOND_PAGES);
> @@ -31,13 +34,30 @@ bool init_domheap_mappings(unsigned int cpu)
> {
> unsigned int order = get_order_from_pages(DOMHEAP_SECOND_PAGES);
> lpae_t *root = per_cpu(xen_pgtable, cpu);
> + lpae_t *first;
> unsigned int i, first_idx;
> lpae_t *domheap;
> mfn_t mfn;
>
> + /* Convenience aliases */
> + DECLARE_OFFSETS(offsets, DOMHEAP_VIRT_START);
> +
> ASSERT(root);
> ASSERT(!per_cpu(xen_dommap, cpu));
>
> + /*
> + * On Arm64, the root is at level 0. Therefore we need an extra step
> + * to allocate the first level page-table.
> + */
> +#ifdef CONFIG_ARM_64
> + if ( create_xen_table(&root[offsets[0]]) )
> + return false;
> +
> + first = xen_map_table(lpae_get_mfn(root[offsets[0]]));
> +#else
> + first = root;
> +#endif
> +
> /*
> * The domheap for cpu0 is initialized before the heap is initialized.
> * So we need to use pre-allocated pages.
> @@ -58,16 +78,20 @@ bool init_domheap_mappings(unsigned int cpu)
> * domheap mapping pages.
> */
> mfn = virt_to_mfn(domheap);
> - first_idx = first_table_offset(DOMHEAP_VIRT_START);
> + first_idx = offsets[1];
> for ( i = 0; i < DOMHEAP_SECOND_PAGES; i++ )
> {
> lpae_t pte = mfn_to_xen_entry(mfn_add(mfn, i), MT_NORMAL);
> pte.pt.table = 1;
> - write_pte(&root[first_idx + i], pte);
> + write_pte(&first[first_idx + i], pte);
> }
>
> per_cpu(xen_dommap, cpu) = domheap;
>
> +#ifdef CONFIG_ARM_64
> + xen_unmap_table(first);
> +#endif
> +
> return true;
> }
>
> @@ -91,6 +115,10 @@ void *map_domain_page(mfn_t mfn)
> lpae_t pte;
> int i, slot;
>
> + /* Bypass the mapcache if the page is in the directmap */
> + if ( arch_mfns_in_directmap(mfn_x(mfn), 1) )
> + return mfn_to_virt(mfn);
> +
> local_irq_save(flags);
>
> /* The map is laid out as an open-addressed hash table where each
> @@ -151,15 +179,24 @@ void *map_domain_page(mfn_t mfn)
> }
>
> /* Release a mapping taken with map_domain_page() */
> -void unmap_domain_page(const void *va)
> +void unmap_domain_page(const void *ptr)
> {
> + unsigned long va = (unsigned long)ptr;
> unsigned long flags;
> lpae_t *map = this_cpu(xen_dommap);
> - int slot = ((unsigned long) va - DOMHEAP_VIRT_START) >> SECOND_SHIFT;
> + unsigned int slot;
>
> - if ( !va )
> + /*
> + * map_domain_page() may not have mapped anything if the address
> + * is part of the directmap. So ignore anything outside of the
> + * domheap.
> + */
> + if ( (va < DOMHEAP_VIRT_START) ||
> + ((va - DOMHEAP_VIRT_START) >= DOMHEAP_VIRT_SIZE) )
> return;
>
> + slot = (va - DOMHEAP_VIRT_START) >> SECOND_SHIFT;
> +
> local_irq_save(flags);
>
> ASSERT(slot >= 0 && slot < DOMHEAP_ENTRIES);
> diff --git a/xen/arch/arm/include/asm/config.h
> b/xen/arch/arm/include/asm/config.h
> index 0fefed1b8aa9..12b7f1f1b9ea 100644
> --- a/xen/arch/arm/include/asm/config.h
> +++ b/xen/arch/arm/include/asm/config.h
> @@ -156,6 +156,13 @@
> #define FRAMETABLE_SIZE GB(32)
> #define FRAMETABLE_NR (FRAMETABLE_SIZE / sizeof(*frame_table))
>
> +#define DOMHEAP_VIRT_START SLOT0(255)
> +#define DOMHEAP_VIRT_SIZE GB(2)
> +
> +#define DOMHEAP_ENTRIES 1024 /* 1024 2MB mapping slots */
> +/* Number of domheap pagetable pages required at the second level (2MB
> mappings) */
> +#define DOMHEAP_SECOND_PAGES (DOMHEAP_VIRT_SIZE >> FIRST_SHIFT)
> +
> #define DIRECTMAP_VIRT_START SLOT0(256)
> #define DIRECTMAP_SIZE (SLOT0_ENTRY_SIZE * (265-256))
> #define DIRECTMAP_VIRT_END (DIRECTMAP_VIRT_START + DIRECTMAP_SIZE - 1)
> diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h
> index 7a2c775f9562..d73abf1bf763 100644
> --- a/xen/arch/arm/include/asm/mm.h
> +++ b/xen/arch/arm/include/asm/mm.h
> @@ -416,6 +416,11 @@ static inline bool arch_has_directmap(void)
> return true;
> }
>
> +/* Helpers to allocate, map and unmap a Xen page-table */
> +int create_xen_table(lpae_t *entry);
> +lpae_t *xen_map_table(mfn_t mfn);
> +void xen_unmap_table(const lpae_t *table);
> +
> #endif /* __ARCH_ARM_MM__ */
> /*
> * Local variables:
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index 2af751af9003..f5fb957554a5 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -177,7 +177,7 @@ static void __init __maybe_unused build_assertions(void)
> #undef CHECK_SAME_SLOT
> }
>
> -static lpae_t *xen_map_table(mfn_t mfn)
> +lpae_t *xen_map_table(mfn_t mfn)
> {
> /*
> * During early boot, map_domain_page() may be unusable. Use the
> @@ -189,7 +189,7 @@ static lpae_t *xen_map_table(mfn_t mfn)
> return map_domain_page(mfn);
> }
>
> -static void xen_unmap_table(const lpae_t *table)
> +void xen_unmap_table(const lpae_t *table)
> {
> /*
> * During early boot, xen_map_table() will not use map_domain_page()
> @@ -699,7 +699,7 @@ void *ioremap(paddr_t pa, size_t len)
> return ioremap_attr(pa, len, PAGE_HYPERVISOR_NOCACHE);
> }
>
> -static int create_xen_table(lpae_t *entry)
> +int create_xen_table(lpae_t *entry)
> {
> mfn_t mfn;
> void *p;
> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> index 88d9d90fb5ad..b1a8f91bb385 100644
> --- a/xen/arch/arm/setup.c
> +++ b/xen/arch/arm/setup.c
> @@ -923,6 +923,10 @@ static void __init setup_mm(void)
> */
> populate_boot_allocator();
>
> + if ( !init_domheap_mappings(smp_processor_id()) )
> + panic("CPU%u: Unable to prepare the domheap page-tables\n",
> + smp_processor_id());
> +
> total_pages = 0;
>
> for ( i = 0; i < banks->nr_banks; i++ )
> --
> 2.38.1
>
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