On 13/07/16 02:59, Andre Przywara wrote:
> Add emulation for some basic MMIO registers used in the ITS emulation.
> This includes:
> - GITS_{CTLR,TYPER,IIDR}
> - ID registers
> - GITS_{CBASER,CREADR,CWRITER}
> (which implement the ITS command buffer handling)
> - GITS_BASER<n>
>
> Most of the handlers are pretty straight forward, only the CWRITER
> handler is a bit more involved by taking the new its_cmd mutex and
> then iterating over the command buffer.
> The registers holding base addresses and attributes are sanitised before
> storing them.
>
> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
> ---
> include/kvm/arm_vgic.h | 16 ++
> virt/kvm/arm/vgic/vgic-its.c | 394 ++++++++++++++++++++++++++++++++++++++-
> virt/kvm/arm/vgic/vgic-mmio-v3.c | 8 +-
> virt/kvm/arm/vgic/vgic-mmio.h | 6 +
> virt/kvm/arm/vgic/vgic.c | 12 +-
> 5 files changed, 419 insertions(+), 17 deletions(-)
>
> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> index 8609fac..6186749 100644
> --- a/include/kvm/arm_vgic.h
> +++ b/include/kvm/arm_vgic.h
> @@ -22,6 +22,7 @@
> #include <linux/spinlock.h>
> #include <linux/types.h>
> #include <kvm/iodev.h>
> +#include <linux/list.h>
>
> #define VGIC_V3_MAX_CPUS 255
> #define VGIC_V2_MAX_CPUS 8
> @@ -136,6 +137,21 @@ struct vgic_its {
> bool enabled;
> bool initialized;
> struct vgic_io_device iodev;
> +
> + /* These registers correspond to GITS_BASER{0,1} */
> + u64 baser_device_table;
> + u64 baser_coll_table;
> +
> + /* Protects the command queue */
> + struct mutex cmd_lock;
> + u64 cbaser;
> + u32 creadr;
> + u32 cwriter;
> +
> + /* Protects the device and collection lists */
> + struct mutex its_lock;
> + struct list_head device_list;
> + struct list_head collection_list;
> };
>
> struct vgic_dist {
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index 393ad3a..dc9a98f 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -21,6 +21,7 @@
> #include <linux/kvm.h>
> #include <linux/kvm_host.h>
> #include <linux/interrupt.h>
> +#include <linux/list.h>
> #include <linux/uaccess.h>
>
> #include <linux/irqchip/arm-gic-v3.h>
> @@ -32,6 +33,326 @@
> #include "vgic.h"
> #include "vgic-mmio.h"
>
> +struct its_device {
> + struct list_head dev_list;
> +
> + /* the head for the list of ITTEs */
> + struct list_head itt_head;
> + u32 device_id;
> +};
> +
> +#define COLLECTION_NOT_MAPPED ((u32)~0)
> +
> +struct its_collection {
> + struct list_head coll_list;
> +
> + u32 collection_id;
> + u32 target_addr;
> +};
> +
> +#define its_is_collection_mapped(coll) ((coll) && \
> + ((coll)->target_addr != COLLECTION_NOT_MAPPED))
> +
> +struct its_itte {
> + struct list_head itte_list;
> +
> + struct its_collection *collection;
> + u32 lpi;
> + u32 event_id;
> +};
> +
> +#define CBASER_ADDRESS(x) ((x) & GENMASK_ULL(51, 12))
I thought we had agreed on sticking to 48bit all over the place?
> +
> +static unsigned long vgic_mmio_read_its_ctlr(struct kvm *vcpu,
> + struct vgic_its *its,
> + gpa_t addr, unsigned int len)
> +{
> + u32 reg = 0;
> +
> + mutex_lock(&its->cmd_lock);
> + if (its->creadr == its->cwriter)
> + reg |= GITS_CTLR_QUIESCENT;
> + if (its->enabled)
> + reg |= GITS_CTLR_ENABLE;
> + mutex_unlock(&its->cmd_lock);
> +
> + return reg;
> +}
> +
> +static void vgic_mmio_write_its_ctlr(struct kvm *kvm, struct vgic_its *its,
> + gpa_t addr, unsigned int len,
> + unsigned long val)
> +{
> + its->enabled = !!(val & GITS_CTLR_ENABLE);
> +}
> +
> +static unsigned long vgic_mmio_read_its_typer(struct kvm *kvm,
> + struct vgic_its *its,
> + gpa_t addr, unsigned int len)
> +{
> + u64 reg = GITS_TYPER_PLPIS;
> +
> + /*
> + * We use linear CPU numbers for redistributor addressing,
> + * so GITS_TYPER.PTA is 0.
> + * Also we force all PROPBASER registers to be the same, so
> + * CommonLPIAff is 0 as well.
> + * To avoid memory waste in the guest, we keep the number of IDBits and
> + * DevBits low - as least for the time being.
> + */
> + reg |= 0x0f << GITS_TYPER_DEVBITS_SHIFT;
> + reg |= 0x0f << GITS_TYPER_IDBITS_SHIFT;
> +
> + return extract_bytes(reg, addr & 7, len);
> +}
> +
> +static unsigned long vgic_mmio_read_its_iidr(struct kvm *kvm,
> + struct vgic_its *its,
> + gpa_t addr, unsigned int len)
> +{
> + return (PRODUCT_ID_KVM << 24) | (IMPLEMENTER_ARM << 0);
> +}
> +
> +static unsigned long vgic_mmio_read_its_idregs(struct kvm *kvm,
> + struct vgic_its *its,
> + gpa_t addr, unsigned int len)
> +{
> + switch (addr & 0xffff) {
> + case GITS_PIDR0:
> + return 0x92; /* part number, bits[7:0] */
> + case GITS_PIDR1:
> + return 0xb4; /* part number, bits[11:8] */
> + case GITS_PIDR2:
> + return GIC_PIDR2_ARCH_GICv3 | 0x0b;
> + case GITS_PIDR4:
> + return 0x40; /* This is a 64K software visible page */
> + /* The following are the ID registers for (any) GIC. */
> + case GITS_CIDR0:
> + return 0x0d;
> + case GITS_CIDR1:
> + return 0xf0;
> + case GITS_CIDR2:
> + return 0x05;
> + case GITS_CIDR3:
> + return 0xb1;
> + }
> +
> + return 0;
> +}
> +
> +/* Requires the its_lock to be held. */
> +static void its_free_itte(struct kvm *kvm, struct its_itte *itte)
> +{
> + list_del(&itte->itte_list);
> + kfree(itte);
> +}
> +
> +static int vgic_its_handle_command(struct kvm *kvm, struct vgic_its *its,
> + u64 *its_cmd)
> +{
> + return -ENODEV;
> +}
> +
> +static u64 vgic_sanitise_its_baser(u64 reg)
> +{
> + reg = vgic_sanitise_field(reg, GITS_BASER_SHAREABILITY_MASK,
> + GITS_BASER_SHAREABILITY_SHIFT,
> + vgic_sanitise_shareability);
> + reg = vgic_sanitise_field(reg, GITS_BASER_CACHEABILITY_MASK,
> + GITS_BASER_INNER_CACHEABILITY_SHIFT,
> + vgic_sanitise_inner_cacheability);
> + reg = vgic_sanitise_field(reg, GITS_BASER_OUTER_CACHEABILITY_MASK,
> + GITS_BASER_OUTER_CACHEABILITY_SHIFT,
> + vgic_sanitise_outer_cacheability);
> +
> + /* When using 64K pages, we clear bits to limit the PA to 48 bits. */
> + if ((reg & GITS_BASER_PAGE_SIZE_MASK) == GITS_BASER_PAGE_SIZE_64K)
Why that check? We were supposed to only support 64kB pages so that we
could simplify the code. The page size field should be RO, and set to 64k.
> + reg &= ~GENMASK_ULL(15, 12);
> +
> + return reg;
> +}
> +
> +static u64 vgic_sanitise_its_cbaser(u64 reg)
> +{
> + reg = vgic_sanitise_field(reg, GITS_CBASER_SHAREABILITY_MASK,
> + GITS_CBASER_SHAREABILITY_SHIFT,
> + vgic_sanitise_shareability);
> + reg = vgic_sanitise_field(reg, GITS_CBASER_CACHEABILITY_MASK,
> + GITS_CBASER_INNER_CACHEABILITY_SHIFT,
> + vgic_sanitise_inner_cacheability);
> + reg = vgic_sanitise_field(reg, GITS_CBASER_OUTER_CACHEABILITY_MASK,
> + GITS_CBASER_OUTER_CACHEABILITY_SHIFT,
> + vgic_sanitise_outer_cacheability);
> +
> + /*
> + * Sanitise the physical address to be 64k aligned (for 4K and 16K
> + * pages), also limit the physical addresses to 48 bits.
Please drop the remark about 4k and 16k pages, this is irrelevant here.
> + */
> + reg &= ~(GENMASK_ULL(51, 48) | GENMASK_ULL(15, 12));
> +
> + return reg;
> +}
> +
> +static unsigned long vgic_mmio_read_its_cbaser(struct kvm *kvm,
> + struct vgic_its *its,
> + gpa_t addr, unsigned int len)
> +{
> + return extract_bytes(its->cbaser, addr & 7, len);
> +}
> +
> +static void vgic_mmio_write_its_cbaser(struct kvm *kvm, struct vgic_its *its,
> + gpa_t addr, unsigned int len,
> + unsigned long val)
> +{
> + /* When GITS_CTLR.Enable is 1, this register is RO. */
> + if (its->enabled)
> + return;
> +
> + mutex_lock(&its->cmd_lock);
> + its->cbaser = update_64bit_reg(its->cbaser, addr & 7, len, val);
> + its->cbaser = vgic_sanitise_its_cbaser(its->cbaser);
> + its->creadr = 0;
> + /*
> + * CWRITER is architecturally UNKNOWN on reset, but we need to reset
> + * it to CREADR to make sure we start with an empty command buffer.
> + */
> + its->cwriter = its->creadr;
> + mutex_unlock(&its->cmd_lock);
> +}
> +
> +#define ITS_CMD_BUFFER_SIZE(baser) ((((baser) & 0xff) + 1) << 12)
> +#define ITS_CMD_SIZE 32
> +
> +/*
> + * By writing to CWRITER the guest announces new commands to be processed.
> + * To avoid any races in the first place, we take the its_cmd lock, which
> + * protects our ring buffer variables, so that there is only one user
> + * per ITS handling commands at a given time.
> + */
> +static void vgic_mmio_write_its_cwriter(struct kvm *kvm, struct vgic_its *its,
> + gpa_t addr, unsigned int len,
> + unsigned long val)
> +{
> + gpa_t cbaser;
> + u64 cmd_buf[4];
> + u32 reg;
> +
> + if (!its)
> + return;
> +
> + cbaser = CBASER_ADDRESS(its->cbaser);
> +
> + reg = update_64bit_reg(its->cwriter & 0xfffe0, addr & 7, len, val);
> + reg &= 0xfffe0;
Why not use GENMASK to define the valid bits like we did everywhere
else? Also, do you really need this mask in the call to update_64bit_reg?
> + if (reg > ITS_CMD_BUFFER_SIZE(its->cbaser))
> + return;
> +
> + mutex_lock(&its->cmd_lock);
> +
> + its->cwriter = reg;
> +
> + while (its->cwriter != its->creadr) {
> + int ret = kvm_read_guest(kvm, cbaser + its->creadr,
> + cmd_buf, ITS_CMD_SIZE);
> + /*
> + * If kvm_read_guest() fails, this could be due to the guest
> + * programming a bogus value in CBASER or something else going
> + * wrong from which we cannot easily recover.
> + * We just ignore that command then.
It would be good to mention that this is consistent with the handling of
command errors as described in section 6.3.2 of the architecture
specification.
> + */
> + if (!ret)
> + vgic_its_handle_command(kvm, its, cmd_buf);
> +
> + its->creadr += ITS_CMD_SIZE;
> + if (its->creadr == ITS_CMD_BUFFER_SIZE(its->cbaser))
> + its->creadr = 0;
> + }
> +
> + mutex_unlock(&its->cmd_lock);
> +}
> +
> +static unsigned long vgic_mmio_read_its_cwriter(struct kvm *kvm,
> + struct vgic_its *its,
> + gpa_t addr, unsigned int len)
> +{
> + return extract_bytes(its->cwriter & 0xfffe0, addr & 0x7, len);
> +}
> +
> +static unsigned long vgic_mmio_read_its_creadr(struct kvm *kvm,
> + struct vgic_its *its,
> + gpa_t addr, unsigned int len)
> +{
> + return extract_bytes(its->creadr & 0xfffe0, addr & 0x7, len);
> +}
> +
> +#define BASER_INDEX(addr) (((addr) / sizeof(u64)) & 0x7)
> +static unsigned long vgic_mmio_read_its_baser(struct kvm *kvm,
> + struct vgic_its *its,
> + gpa_t addr, unsigned int len)
> +{
> + u64 reg;
> +
> + switch (BASER_INDEX(addr)) {
> + case 0:
> + reg = its->baser_device_table;
> + break;
> + case 1:
> + reg = its->baser_coll_table;
> + break;
> + default:
> + reg = 0;
> + break;
> + }
> +
> + return extract_bytes(reg, addr & 7, len);
> +}
> +
> +#define GITS_BASER_RO_MASK (GENMASK_ULL(52, 48) | GENMASK_ULL(58, 56))
> +static void vgic_mmio_write_its_baser(struct kvm *kvm,
> + struct vgic_its *its,
> + gpa_t addr, unsigned int len,
> + unsigned long val)
> +{
> + u64 entry_size, device_type;
> + u64 reg, *regptr, clearbits = 0;
> +
> + /* When GITS_CTLR.Enable is 1, we ignore write accesses. */
> + if (its->enabled)
> + return;
> +
> + switch (BASER_INDEX(addr)) {
> + case 0:
> + regptr = &its->baser_device_table;
> + entry_size = 8;
> + device_type = GITS_BASER_TYPE_DEVICE;
> + break;
> + case 1:
> + regptr = &its->baser_coll_table;
> + entry_size = 8;
> + device_type = GITS_BASER_TYPE_COLLECTION;
> + clearbits = GITS_BASER_INDIRECT;
> + break;
> + default:
> + return;
> + }
> +
> + reg = update_64bit_reg(*regptr, addr & 7, len, val);
> + reg &= ~GITS_BASER_RO_MASK;
> + reg &= ~clearbits;
> +
> + /*
> + * When the guest wants to use 64K pages, bits 15:12 contain bits 51:48
> + * of the PA, which we don't support. Clear them to emulate RAZ/WI.
> + */
> + if (reg & GITS_BASER_PAGE_SIZE_64K)
> + reg &= ~GENMASK_ULL(15, 12);
Again, this is not what I thought we had agreed on. What I'd like to see
is an ITS that *only* supports 64kB pages, and nothing else. It
simplifies the code, and is consistent with the rest of vgic where we
choose a configuration.
Please drop all support for 4k and 16k pages, and make the page size
field RO.
> + reg |= (entry_size - 1) << GITS_BASER_ENTRY_SIZE_SHIFT;
> + reg |= device_type << GITS_BASER_TYPE_SHIFT;
> + reg = vgic_sanitise_its_baser(reg);
> +
> + *regptr = reg;
> +}
> +
> #define REGISTER_ITS_DESC(off, rd, wr, length, acc) \
> { \
> .reg_offset = off, \
> @@ -41,8 +362,8 @@
> .its_write = wr, \
> }
>
> -static unsigned long its_mmio_read_raz(struct kvm *kvm, struct vgic_its *its,
> - gpa_t addr, unsigned int len)
> +unsigned long its_mmio_read_raz(struct kvm *kvm, struct vgic_its *its,
> + gpa_t addr, unsigned int len)
> {
> return 0;
> }
> @@ -55,28 +376,28 @@ static void its_mmio_write_wi(struct kvm *kvm, struct vgic_its *its,
>
> static struct vgic_register_region its_registers[] = {
> REGISTER_ITS_DESC(GITS_CTLR,
> - its_mmio_read_raz, its_mmio_write_wi, 4,
> + vgic_mmio_read_its_ctlr, vgic_mmio_write_its_ctlr, 4,
> VGIC_ACCESS_32bit),
> REGISTER_ITS_DESC(GITS_IIDR,
> - its_mmio_read_raz, its_mmio_write_wi, 4,
> + vgic_mmio_read_its_iidr, its_mmio_write_wi, 4,
> VGIC_ACCESS_32bit),
> REGISTER_ITS_DESC(GITS_TYPER,
> - its_mmio_read_raz, its_mmio_write_wi, 8,
> + vgic_mmio_read_its_typer, its_mmio_write_wi, 8,
> VGIC_ACCESS_64bit | VGIC_ACCESS_32bit),
> REGISTER_ITS_DESC(GITS_CBASER,
> - its_mmio_read_raz, its_mmio_write_wi, 8,
> + vgic_mmio_read_its_cbaser, vgic_mmio_write_its_cbaser, 8,
> VGIC_ACCESS_64bit | VGIC_ACCESS_32bit),
> REGISTER_ITS_DESC(GITS_CWRITER,
> - its_mmio_read_raz, its_mmio_write_wi, 8,
> + vgic_mmio_read_its_cwriter, vgic_mmio_write_its_cwriter, 8,
> VGIC_ACCESS_64bit | VGIC_ACCESS_32bit),
> REGISTER_ITS_DESC(GITS_CREADR,
> - its_mmio_read_raz, its_mmio_write_wi, 8,
> + vgic_mmio_read_its_creadr, its_mmio_write_wi, 8,
> VGIC_ACCESS_64bit | VGIC_ACCESS_32bit),
> REGISTER_ITS_DESC(GITS_BASER,
> - its_mmio_read_raz, its_mmio_write_wi, 0x40,
> + vgic_mmio_read_its_baser, vgic_mmio_write_its_baser, 0x40,
> VGIC_ACCESS_64bit | VGIC_ACCESS_32bit),
> REGISTER_ITS_DESC(GITS_IDREGS_BASE,
> - its_mmio_read_raz, its_mmio_write_wi, 0x30,
> + vgic_mmio_read_its_idregs, its_mmio_write_wi, 0x30,
> VGIC_ACCESS_32bit),
> };
>
> @@ -100,6 +421,18 @@ static int vgic_its_register(struct kvm *kvm, struct vgic_its *its)
> return ret;
> }
>
> +#define INITIAL_BASER_VALUE \
> + (GIC_BASER_CACHEABILITY(GITS_BASER, INNER, RaWb) | \
> + GIC_BASER_CACHEABILITY(GITS_BASER, OUTER, SameAsInner) | \
> + GIC_BASER_SHAREABILITY(GITS_BASER, InnerShareable) | \
> + ((8ULL - 1) << GITS_BASER_ENTRY_SIZE_SHIFT) | \
> + GITS_BASER_PAGE_SIZE_64K)
> +
> +#define INITIAL_PROPBASER_VALUE \
> + (GIC_BASER_CACHEABILITY(GICR_PROPBASER, INNER, RaWb) | \
> + GIC_BASER_CACHEABILITY(GICR_PROPBASER, OUTER, SameAsInner) | \
> + GIC_BASER_SHAREABILITY(GICR_PROPBASER, InnerShareable))
> +
> static int vgic_its_create(struct kvm_device *dev, u32 type)
> {
> struct vgic_its *its;
> @@ -111,12 +444,24 @@ static int vgic_its_create(struct kvm_device *dev, u32 type)
> if (!its)
> return -ENOMEM;
>
> + mutex_init(&its->its_lock);
> + mutex_init(&its->cmd_lock);
> +
> its->vgic_its_base = VGIC_ADDR_UNDEF;
>
> + INIT_LIST_HEAD(&its->device_list);
> + INIT_LIST_HEAD(&its->collection_list);
> +
> dev->kvm->arch.vgic.has_its = true;
> its->initialized = false;
> its->enabled = false;
>
> + its->baser_device_table = INITIAL_BASER_VALUE |
> + ((u64)GITS_BASER_TYPE_DEVICE << GITS_BASER_TYPE_SHIFT);
> + its->baser_coll_table = INITIAL_BASER_VALUE |
> + ((u64)GITS_BASER_TYPE_COLLECTION << GITS_BASER_TYPE_SHIFT);
> + dev->kvm->arch.vgic.propbaser = INITIAL_PROPBASER_VALUE;
> +
> dev->private = its;
>
> return 0;
> @@ -124,7 +469,36 @@ static int vgic_its_create(struct kvm_device *dev, u32 type)
>
> static void vgic_its_destroy(struct kvm_device *kvm_dev)
> {
> + struct kvm *kvm = kvm_dev->kvm;
> struct vgic_its *its = kvm_dev->private;
> + struct its_device *dev;
> + struct its_itte *itte;
> + struct list_head *dev_cur, *dev_temp;
> + struct list_head *cur, *temp;
> +
> + /*
> + * We may end up here without the lists ever having been initialized.
> + * Check this and bail out early to avoid dereferencing a NULL pointer.
> + */
> + if (!its->device_list.next)
> + return;
> +
> + mutex_lock(&its->its_lock);
> + list_for_each_safe(dev_cur, dev_temp, &its->device_list) {
> + dev = container_of(dev_cur, struct its_device, dev_list);
> + list_for_each_safe(cur, temp, &dev->itt_head) {
> + itte = (container_of(cur, struct its_itte, itte_list));
> + its_free_itte(kvm, itte);
> + }
> + list_del(dev_cur);
> + kfree(dev);
> + }
> +
> + list_for_each_safe(cur, temp, &its->collection_list) {
> + list_del(cur);
> + kfree(container_of(cur, struct its_collection, coll_list));
> + }
> + mutex_unlock(&its->its_lock);
>
> kfree(its);
> }
> diff --git a/virt/kvm/arm/vgic/vgic-mmio-v3.c b/virt/kvm/arm/vgic/vgic-mmio-v3.c
> index 6cb52dd..d98e009 100644
> --- a/virt/kvm/arm/vgic/vgic-mmio-v3.c
> +++ b/virt/kvm/arm/vgic/vgic-mmio-v3.c
> @@ -23,15 +23,15 @@
> #include "vgic-mmio.h"
>
> /* extract @num bytes at @offset bytes offset in data */
> -static unsigned long extract_bytes(unsigned long data, unsigned int offset,
> - unsigned int num)
> +unsigned long extract_bytes(unsigned long data, unsigned int offset,
> + unsigned int num)
> {
> return (data >> (offset * 8)) & GENMASK_ULL(num * 8 - 1, 0);
> }
>
> /* allows updates of any half of a 64-bit register (or the whole thing) */
> -static u64 update_64bit_reg(u64 reg, unsigned int offset, unsigned int len,
> - unsigned long val)
> +u64 update_64bit_reg(u64 reg, unsigned int offset, unsigned int len,
> + unsigned long val)
> {
> int lower = (offset & 4) * 8;
> int upper = lower + 8 * len - 1;
> diff --git a/virt/kvm/arm/vgic/vgic-mmio.h b/virt/kvm/arm/vgic/vgic-mmio.h
> index 366d663..0b3ecf9 100644
> --- a/virt/kvm/arm/vgic/vgic-mmio.h
> +++ b/virt/kvm/arm/vgic/vgic-mmio.h
> @@ -96,6 +96,12 @@ unsigned long vgic_data_mmio_bus_to_host(const void *val, unsigned int len);
> void vgic_data_host_to_mmio_bus(void *buf, unsigned int len,
> unsigned long data);
>
> +unsigned long extract_bytes(unsigned long data, unsigned int offset,
> + unsigned int num);
> +
> +u64 update_64bit_reg(u64 reg, unsigned int offset, unsigned int len,
> + unsigned long val);
> +
> unsigned long vgic_mmio_read_raz(struct kvm_vcpu *vcpu,
> gpa_t addr, unsigned int len);
>
> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> index 1fb2693..d7ea5df 100644
> --- a/virt/kvm/arm/vgic/vgic.c
> +++ b/virt/kvm/arm/vgic/vgic.c
> @@ -33,10 +33,16 @@ struct vgic_global __section(.hyp.text) kvm_vgic_global_state;
>
> /*
> * Locking order is always:
> - * vgic_cpu->ap_list_lock
> - * vgic_irq->irq_lock
> + * its->cmd_lock (mutex)
> + * its->its_lock (mutex)
> + * vgic_cpu->ap_list_lock
> + * vgic_irq->irq_lock
> *
> - * (that is, always take the ap_list_lock before the struct vgic_irq lock).
> + * If you need to take multiple locks, always take the upper lock first,
> + * then the lower ones, e.g. first take the its_lock, then the irq_lock.
> + * If you are already holding a lock and need to take a higher one, you
> + * have to drop the lower ranking lock first and re-aquire it after having
> + * taken the upper one.
> *
> * When taking more than one ap_list_lock at the same time, always take the
> * lowest numbered VCPU's ap_list_lock first, so:
>
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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