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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v6 07/36] ARM: GICv3 ITS: introduce host LPI array
On Fri, 7 Apr 2017, Andre Przywara wrote:
> The number of LPIs on a host can be potentially huge (millions),
> although in practise will be mostly reasonable. So prematurely allocating
> an array of struct irq_desc's for each LPI is not an option.
> However Xen itself does not care about LPIs, as every LPI will be injected
> into a guest (Dom0 for now).
> Create a dense data structure (8 Bytes) for each LPI which holds just
> enough information to determine the virtual IRQ number and the VCPU into
> which the LPI needs to be injected.
> Also to not artificially limit the number of LPIs, we create a 2-level
> table for holding those structures.
> This patch introduces functions to initialize these tables and to
> create, lookup and destroy entries for a given LPI.
> By using the naturally atomic access guarantee the native uint64_t data
> type gives us, we allocate and access LPI information in a way that does
> not require a lock.
>
> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> ---
> xen/arch/arm/gic-v3-lpi.c | 230
> +++++++++++++++++++++++++++++++++++++++
> xen/include/asm-arm/gic_v3_its.h | 6 +
> xen/include/asm-arm/irq.h | 8 ++
> 3 files changed, 244 insertions(+)
>
> diff --git a/xen/arch/arm/gic-v3-lpi.c b/xen/arch/arm/gic-v3-lpi.c
> index d8a4f5a..292f2d0 100644
> --- a/xen/arch/arm/gic-v3-lpi.c
> +++ b/xen/arch/arm/gic-v3-lpi.c
> @@ -20,14 +20,37 @@
>
> #include <xen/lib.h>
> #include <xen/mm.h>
> +#include <xen/sched.h>
> #include <xen/sizes.h>
> #include <xen/warning.h>
> +#include <asm/atomic.h>
> +#include <asm/domain.h>
> #include <asm/gic.h>
> #include <asm/gic_v3_defs.h>
> #include <asm/gic_v3_its.h>
> #include <asm/io.h>
> #include <asm/page.h>
>
> +/*
> + * There could be a lot of LPIs on the host side, and they always go to
> + * a guest. So having a struct irq_desc for each of them would be wasteful
> + * and useless.
> + * Instead just store enough information to find the right VCPU to inject
> + * those LPIs into, which just requires the virtual LPI number.
> + * To avoid a global lock on this data structure, this is using a lockless
> + * approach relying on the architectural atomicity of native data types:
> + * We read or write the "data" view of this union atomically, then can
> + * access the broken-down fields in our local copy.
> + */
> +union host_lpi {
> + uint64_t data;
> + struct {
> + uint32_t virt_lpi;
> + uint16_t dom_id;
> + uint16_t vcpu_id;
> + };
> +};
> +
> #define LPI_PROPTABLE_NEEDS_FLUSHING (1U << 0)
>
> /* Global state */
> @@ -35,12 +58,23 @@ static struct {
> /* The global LPI property table, shared by all redistributors. */
> uint8_t *lpi_property;
> /*
> + * A two-level table to lookup LPIs firing on the host and look up the
> + * VCPU and virtual LPI number to inject into.
> + */
> + union host_lpi **host_lpis;
> + /*
> * Number of physical LPIs the host supports. This is a property of
> * the GIC hardware. We depart from the habit of naming these things
> * "physical" in Xen, as the GICv3/4 spec uses the term "physical LPI"
> * in a different context to differentiate them from "virtual LPIs".
> */
> unsigned long int max_host_lpi_ids;
> + /*
> + * Protects allocation and deallocation of host LPIs and next_free_lpi,
> + * but not the actual data stored in the host_lpi entry.
> + */
> + spinlock_t host_lpis_lock;
> + uint32_t next_free_lpi;
> unsigned int flags;
> } lpi_data;
>
> @@ -53,6 +87,28 @@ struct lpi_redist_data {
> static DEFINE_PER_CPU(struct lpi_redist_data, lpi_redist);
>
> #define MAX_NR_HOST_LPIS (lpi_data.max_host_lpi_ids - LPI_OFFSET)
> +#define HOST_LPIS_PER_PAGE (PAGE_SIZE / sizeof(union host_lpi))
> +
> +static union host_lpi *gic_get_host_lpi(uint32_t plpi)
> +{
> + union host_lpi *block;
> +
> + if ( !is_lpi(plpi) || plpi >= MAX_NR_HOST_LPIS + LPI_OFFSET )
> + return NULL;
> +
> + ASSERT(plpi >= LPI_OFFSET);
> +
> + plpi -= LPI_OFFSET;
> +
> + block = lpi_data.host_lpis[plpi / HOST_LPIS_PER_PAGE];
> + if ( !block )
> + return NULL;
> +
> + /* Matches the write barrier in allocation code. */
> + smp_rmb();
> +
> + return &block[plpi % HOST_LPIS_PER_PAGE];
> +}
>
> /*
> * An ITS can refer to redistributors in two ways: either by an ID (possibly
> @@ -220,8 +276,18 @@ int gicv3_lpi_init_rdist(void __iomem * rdist_base)
> static unsigned int max_lpi_bits = 20;
> integer_param("max_lpi_bits", max_lpi_bits);
>
> +/*
> + * Allocate the 2nd level array for host LPIs. This one holds pointers
> + * to the page with the actual "union host_lpi" entries. Our LPI limit
> + * avoids excessive memory usage.
> + */
> int gicv3_lpi_init_host_lpis(unsigned int host_lpi_bits)
> {
> + unsigned int nr_lpi_ptrs;
> +
> + /* We rely on the data structure being atomically accessible. */
> + BUILD_BUG_ON(sizeof(union host_lpi) > sizeof(unsigned long));
> +
> /*
> * An implementation needs to support at least 14 bits of LPI IDs.
> * Tell the user about it, the actual number is reported below.
> @@ -240,11 +306,175 @@ int gicv3_lpi_init_host_lpis(unsigned int
> host_lpi_bits)
> if ( lpi_data.max_host_lpi_ids > BIT(24) )
> warning_add("Using high number of LPIs, limit memory usage with
> max_lpi_bits\n");
>
> + spin_lock_init(&lpi_data.host_lpis_lock);
> + lpi_data.next_free_lpi = 0;
> +
> + nr_lpi_ptrs = MAX_NR_HOST_LPIS / (PAGE_SIZE / sizeof(union host_lpi));
> + lpi_data.host_lpis = xzalloc_array(union host_lpi *, nr_lpi_ptrs);
> + if ( !lpi_data.host_lpis )
> + return -ENOMEM;
> +
> printk("GICv3: using at most %lu LPIs on the host.\n", MAX_NR_HOST_LPIS);
>
> return 0;
> }
>
> +static int find_unused_host_lpi(uint32_t start, uint32_t *index)
> +{
> + unsigned int chunk;
> + uint32_t i = *index;
> +
> + ASSERT(spin_is_locked(&lpi_data.host_lpis_lock));
> +
> + for ( chunk = start;
> + chunk < MAX_NR_HOST_LPIS / HOST_LPIS_PER_PAGE;
> + chunk++ )
> + {
> + /* If we hit an unallocated chunk, use entry 0 in that one. */
> + if ( !lpi_data.host_lpis[chunk] )
> + {
> + *index = 0;
> + return chunk;
> + }
> +
> + /* Find an unallocated entry in this chunk. */
> + for ( ; i < HOST_LPIS_PER_PAGE; i += LPI_BLOCK )
> + {
> + if ( lpi_data.host_lpis[chunk][i].dom_id == DOMID_INVALID )
> + {
> + *index = i;
> + return chunk;
> + }
> + }
> + i = 0;
> + }
> +
> + return -1;
> +}
> +
> +/*
> + * Allocate a block of 32 LPIs on the given host ITS for device "devid",
> + * starting with "eventid". Put them into the respective ITT by issuing a
> + * MAPTI command for each of them.
> + */
> +int gicv3_allocate_host_lpi_block(struct domain *d, uint32_t *first_lpi)
> +{
> + uint32_t lpi, lpi_idx;
> + int chunk;
> + int i;
> +
> + spin_lock(&lpi_data.host_lpis_lock);
> + lpi_idx = lpi_data.next_free_lpi % HOST_LPIS_PER_PAGE;
> + chunk = find_unused_host_lpi(lpi_data.next_free_lpi / HOST_LPIS_PER_PAGE,
> + &lpi_idx);
> +
> + if ( chunk == - 1 ) /* rescan for a hole from the beginning */
> + {
> + lpi_idx = 0;
> + chunk = find_unused_host_lpi(0, &lpi_idx);
> + if ( chunk == -1 )
> + {
> + spin_unlock(&lpi_data.host_lpis_lock);
> + return -ENOSPC;
> + }
> + }
> +
> + /* If we hit an unallocated chunk, we initialize it and use entry 0. */
> + if ( !lpi_data.host_lpis[chunk] )
> + {
> + union host_lpi *new_chunk;
> +
> + /* TODO: NUMA locality for quicker IRQ path? */
> + new_chunk = alloc_xenheap_page();
> + if ( !new_chunk )
> + {
> + spin_unlock(&lpi_data.host_lpis_lock);
> + return -ENOMEM;
> + }
> +
> + for ( i = 0; i < HOST_LPIS_PER_PAGE; i += LPI_BLOCK )
> + new_chunk[i].dom_id = DOMID_INVALID;
> +
> + /*
> + * Make sure all slots are really marked empty before publishing the
> + * new chunk.
> + */
> + smp_wmb();
> +
> + lpi_data.host_lpis[chunk] = new_chunk;
> + lpi_idx = 0;
> + }
> +
> + lpi = chunk * HOST_LPIS_PER_PAGE + lpi_idx;
> +
> + for ( i = 0; i < LPI_BLOCK; i++ )
> + {
> + union host_lpi hlpi;
> +
> + /*
> + * Mark this host LPI as belonging to the domain, but don't assign
> + * any virtual LPI or a VCPU yet.
> + */
> + hlpi.virt_lpi = INVALID_LPI;
> + hlpi.dom_id = d->domain_id;
> + hlpi.vcpu_id = INVALID_VCPU_ID;
> + write_u64_atomic(&lpi_data.host_lpis[chunk][lpi_idx + i].data,
> + hlpi.data);
> +
> + /*
> + * Enable this host LPI, so we don't have to do this during the
> + * guest's runtime.
> + */
> + lpi_data.lpi_property[lpi + i] |= LPI_PROP_ENABLED;
> + }
> +
> + lpi_data.next_free_lpi = lpi + LPI_BLOCK;
> +
> + /*
> + * We have allocated and initialized the host LPI entries, so it's safe
> + * to drop the lock now. Access to the structures can be done
> concurrently
> + * as it involves only an atomic uint64_t access.
> + */
> + spin_unlock(&lpi_data.host_lpis_lock);
> +
> + if ( lpi_data.flags & LPI_PROPTABLE_NEEDS_FLUSHING )
> + clean_and_invalidate_dcache_va_range(&lpi_data.lpi_property[lpi],
> + LPI_BLOCK);
> +
> + *first_lpi = lpi + LPI_OFFSET;
> +
> + return 0;
> +}
> +
> +void gicv3_free_host_lpi_block(uint32_t first_lpi)
> +{
> + union host_lpi *hlpi, empty_lpi = { .dom_id = DOMID_INVALID };
> + int i;
> +
> + /* This should only be called with the beginning of a block. */
> + ASSERT((first_lpi % LPI_BLOCK) == 0);
> +
> + hlpi = gic_get_host_lpi(first_lpi);
> + if ( !hlpi )
> + return; /* Nothing to free here. */
> +
> + spin_lock(&lpi_data.host_lpis_lock);
> +
> + for ( i = 0; i < LPI_BLOCK; i++ )
> + write_u64_atomic(&hlpi[i].data, empty_lpi.data);
> +
> + /*
> + * Make sure the next allocation can reuse this block, as we do only
> + * forward scanning when finding an unused block.
> + */
> + if ( lpi_data.next_free_lpi > first_lpi )
> + lpi_data.next_free_lpi = first_lpi;
> +
> + spin_unlock(&lpi_data.host_lpis_lock);
> +
> + return;
> +}
> +
> /*
> * Local variables:
> * mode: C
> diff --git a/xen/include/asm-arm/gic_v3_its.h
> b/xen/include/asm-arm/gic_v3_its.h
> index 13794e0..a96c9dc 100644
> --- a/xen/include/asm-arm/gic_v3_its.h
> +++ b/xen/include/asm-arm/gic_v3_its.h
> @@ -103,6 +103,9 @@
> #define HOST_ITS_FLUSH_CMD_QUEUE (1U << 0)
> #define HOST_ITS_USES_PTA (1U << 1)
>
> +/* We allocate LPIs on the hosts in chunks of 32 to reduce handling
> overhead. */
> +#define LPI_BLOCK 32U
> +
> /* data structure for each hardware ITS */
> struct host_its {
> struct list_head entry;
> @@ -141,6 +144,9 @@ uint64_t gicv3_get_redist_address(unsigned int cpu, bool
> use_pta);
> /* Map a collection for this host CPU to each host ITS. */
> int gicv3_its_setup_collection(unsigned int cpu);
>
> +int gicv3_allocate_host_lpi_block(struct domain *d, uint32_t *first_lpi);
> +void gicv3_free_host_lpi_block(uint32_t first_lpi);
> +
> #else
>
> static inline void gicv3_its_dt_init(const struct dt_device_node *node)
> diff --git a/xen/include/asm-arm/irq.h b/xen/include/asm-arm/irq.h
> index f940092..7c76626 100644
> --- a/xen/include/asm-arm/irq.h
> +++ b/xen/include/asm-arm/irq.h
> @@ -28,6 +28,9 @@ struct arch_irq_desc {
>
> #define LPI_OFFSET 8192
>
> +/* LPIs are always numbered starting at 8192, so 0 is a good invalid case. */
> +#define INVALID_LPI 0
> +
> #define nr_irqs NR_IRQS
> #define nr_static_irqs NR_IRQS
> #define arch_hwdom_irqs(domid) NR_IRQS
> @@ -41,6 +44,11 @@ struct irq_desc *__irq_to_desc(int irq);
>
> void do_IRQ(struct cpu_user_regs *regs, unsigned int irq, int is_fiq);
>
> +static inline bool is_lpi(unsigned int irq)
> +{
> + return irq >= LPI_OFFSET;
> +}
> +
> #define domain_pirq_to_irq(d, pirq) (pirq)
>
> bool_t is_assignable_irq(unsigned int irq);
> --
> 2.9.0
>
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