[PATCH v1 02/17] xen/riscv: add basic VGEIN management for AIA guests

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

It was decided to add support for IMSIC from the start instead of having APLIC
operate in direct delivery mode, as it requires a trap-and-emulation approach,
which is not optimal from a performance standpoint.

AIA provides a hardware-accelerated mechanism for delivering external
interrupts to domains via "guest interrupt files" located in IMSIC.
A single physical hart can implement multiple such files (up to GEILEN),
allowing several virtual harts to receive interrupts directly from hardware.

Introduce per-CPU tracking of guest interrupt file identifiers (VGEIN)
for systems implementing AIA specification. Each CPU maintains
a bitmap describing which guest interrupt files are currently in use.

Add helpers to initialize the bitmap based on the number of available
guest interrupt files (GEILEN), assign a VGEIN to a vCPU, and release it
when no longer needed. When assigning a VGEIN, the corresponding value
is written to the VGEIN field of the guest hstatus register so that
VS-level external interrupts are delivered from the selected interrupt
file.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
Changes in v3:
 - Rephrase per-CPU comment from "Bitmap for each physical cpus..." to
   "VGEIN control structure for each physical CPU...".
 - Use %u for cpu in printk("cpu%u.geilen=%u\n").
 - Fix missing \n in "AIA: failed to init vgein for CPU%u\n".
 - Shorten dprintk message to "vgein_init() failed: %d\n".
 - Use %u instead of %d for v->processor in gprintk() calls.
 - Drop update of ->hstatus in vgein_{assign,release} and let the caller
   to do that. For example, it could be useful in the case of migration
   vCPU from one pCPU to another and so vcpu->hstatus will be updated as a
   last step of this process.
 - Fill ->owners in vgein_{assign,release} just from the start.
---
Changes in v2:
 - add static for defintion of vgein_bmp;
 - Drop declarartion of vgein_bmp from aia.h.
 - Move declaration of 'struct vgein_bmp' from aia.h to aia.c as all the
   management is inside aia.c.
 - Instead of decrement of vgein->geilen just update the wait how it is
   initialized.
 - Return -EOPNOTSUPP in vgein_init() instead of BUG_ON().
 - Use %u to print unsigned int.
 - make bmp field in vgein_bmp not a pointer.
 - allocate owners dynamically.
 - Drop unnessary blank lines.
 - use find_first_zero_bit() instead of bitmap_weight() to find a free slot
   for vgein number.
 - Drop the section number for the comment.
 - Start to search from bitnum 1 for free vgein_id, as bitnum 0 is reserved to
   tell that no guest extrenal interrupt number is used. Thereby drop vgein_id++
   at the end of vgein_assign().
 - s/bitmap_set/__set_bit.
 - s/bitmap_clear/__clear_bit.
 - as vgein_init() is needed to be invoked once per CPU being brought up, drop
   __init for it.
 - Return vgein_id == 0 if vgein_id is higher then maximun supported by h/w
   VGEIN.
 - Add check in vgein_relase() that vgein is 0 and if it is there is nothing
   is needed to do.
 - Use gdprintk instead of printk() in vgein_{assign,release}.
 - Add the claryfing comment above geilen field.
 - Drop ASSERT in vgein_assign() and return just vgein_id = 0 in the case when
   there is no aviablable h/w VGEINs.
 - Make vgein_init() static.
---
---
 xen/arch/riscv/aia.c             | 145 +++++++++++++++++++++++++++++++
 xen/arch/riscv/include/asm/aia.h |   8 ++
 2 files changed, 153 insertions(+)

diff --git a/xen/arch/riscv/aia.c b/xen/arch/riscv/aia.c
index e31c9c2d24b6..4f7f46f58f0b 100644
--- a/xen/arch/riscv/aia.c
+++ b/xen/arch/riscv/aia.c
@@ -1,11 +1,33 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
+#include <xen/bitmap.h>
+#include <xen/cpu.h>
 #include <xen/errno.h>
 #include <xen/init.h>
 #include <xen/sections.h>
+#include <xen/sched.h>
+#include <xen/spinlock.h>
 #include <xen/types.h>
+#include <xen/xvmalloc.h>
 
+#include <asm/aia.h>
 #include <asm/cpufeature.h>
+#include <asm/csr.h>
+#include <asm/current.h>
+
+struct vgein_ctrl {
+    unsigned long bmp;
+    spinlock_t lock;
+    struct vcpu **owners;
+    /* The least-significant bits are implemented first, apart from bit 0 */
+    unsigned int geilen;
+};
+
+/*
+ * VGEIN control structure for each physical CPU to track which VS (guest)
+ * interrupt file IDs are in use.
+ */
+static DEFINE_PER_CPU(struct vgein_ctrl, vgein);
 
 static bool __ro_after_init _aia_usable;
 
@@ -14,10 +36,133 @@ bool aia_usable(void)
     return _aia_usable;
 }
 
+static int vgein_init(unsigned int cpu)
+{
+    struct vgein_ctrl *vgein = &per_cpu(vgein, cpu);
+
+    csr_write(CSR_HGEIE, -1UL);
+    vgein->geilen = flsl(csr_read(CSR_HGEIE) >> 1);
+    csr_write(CSR_HGEIE, 0);
+
+    printk("cpu%u.geilen=%u\n", cpu, vgein->geilen);
+
+    if ( !vgein->geilen )
+        return -EOPNOTSUPP;
+
+    vgein->owners = xvzalloc_array(struct vcpu *, vgein->geilen);
+    if ( !vgein->owners )
+        return -ENOMEM;
+
+    spin_lock_init(&vgein->lock);
+
+    return 0;
+}
+
+static int cf_check cpu_callback(struct notifier_block *nfb, unsigned long 
action,
+                        void *hcpu)
+{
+    unsigned int cpu = (unsigned long)hcpu;
+    int rc = 0;
+
+    switch ( action )
+    {
+    case CPU_STARTING:
+        rc = vgein_init(cpu);
+        if ( rc )
+            printk("AIA: failed to init vgein for CPU%u\n", cpu);
+        break;
+    }
+
+    return notifier_from_errno(rc);
+}
+
+static struct notifier_block cpu_nfb = {
+    .notifier_call = cpu_callback,
+};
+
 void __init aia_init(void)
 {
+    int rc;
+
     if ( !riscv_isa_extension_available(NULL, RISCV_ISA_EXT_ssaia) )
+    {
+        dprintk(XENLOG_WARNING, "SSAIA isn't present in riscv,isa\n");
         return;
+    }
+
+    if ( (rc = vgein_init(0)) )
+    {
+        dprintk(XENLOG_ERR, "vgein_init() failed: %d\n", rc);
+        return;
+    }
 
     _aia_usable = true;
+
+    register_cpu_notifier(&cpu_nfb);
+}
+
+unsigned int vgein_assign(struct vcpu *v)
+{
+    unsigned int vgein_id;
+    struct vgein_ctrl *vgein = &per_cpu(vgein, v->processor);
+    unsigned long *bmp = &vgein->bmp;
+    unsigned long flags;
+
+    if ( !vgein->geilen )
+        return 0;
+
+    spin_lock_irqsave(&vgein->lock, flags);
+    /*
+     * The vgein_id shouldn't be zero, as it will indicate that no guest
+     * external interrupt source is selected for VS-level external interrupts
+     * according to RISC-V privileged spec:
+     *   Hypervisor Status Register (hstatus) in RISC-V privileged spec:
+     *
+     *   The VGEIN (Virtual Guest External Interrupt Number) field selects
+     *   a guest external interrupt source for VS-level external interrupts.
+     *   VGEIN is a WLRL field that must be able to hold values between zero
+     *   and the maximum guest external interrupt number (known as GEILEN),
+     *   inclusive.
+     *   When VGEIN=0, no guest external interrupt source is selected for
+     *   VS-level external interrupts.
+     *
+     * So start to search from bit number 1.
+     */
+    vgein_id = find_next_zero_bit(bmp, vgein->geilen + 1, 1);
+
+    if ( vgein_id > vgein->geilen )
+        vgein_id = 0;
+    else
+    {
+        __set_bit(vgein_id, bmp);
+        vgein->owners[vgein_id] = v;
+    }
+
+    spin_unlock_irqrestore(&vgein->lock, flags);
+
+#ifdef VGEIN_DEBUG
+    gprintk(XENLOG_DEBUG, "%s: %pv: vgein_id(%u), xen_cpu%u_bmp=%#lx\n",
+           __func__, v, vgein_id, v->processor, *bmp);
+#endif
+
+    return vgein_id;
+}
+
+void vgein_release(struct vcpu *v, unsigned int vgein_id)
+{
+    unsigned long flags;
+    struct vgein_ctrl *vgein = &per_cpu(vgein, v->processor);
+
+    if ( !vgein_id )
+        return;
+
+    spin_lock_irqsave(&vgein->lock, flags);
+    __clear_bit(vgein_id, &vgein->bmp);
+    vgein->owners[vgein_id] = NULL;
+    spin_unlock_irqrestore(&vgein->lock, flags);
+
+#ifdef VGEIN_DEBUG
+    gprintk(XENLOG_DEBUG, "%s: vgein_id(%u), xen_cpu%u_bmp=%#lx\n",
+           __func__, vgein_id, v->processor, vgein->bmp);
+#endif
 }
diff --git a/xen/arch/riscv/include/asm/aia.h b/xen/arch/riscv/include/asm/aia.h
index aaa4bf91fc75..c67be0069a1d 100644
--- a/xen/arch/riscv/include/asm/aia.h
+++ b/xen/arch/riscv/include/asm/aia.h
@@ -3,8 +3,16 @@
 #ifndef RISCV_AIA_H
 #define RISCV_AIA_H
 
+#include <xen/percpu.h>
+#include <xen/spinlock.h>
+
+struct vcpu;
+
 bool aia_usable(void);
 
 void aia_init(void);
 
+unsigned int vgein_assign(struct vcpu *v);
+void vgein_release(struct vcpu *v, unsigned int vgein_id);
+
 #endif /* RISCV_AIA_H */
-- 
2.54.0