[PATCH v2 37/39] xen/riscv: map IMSIC interrupt file for vCPUs

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

A guest running in VS-mode expects its own IMSIC S-file at offset 0 of its
guest-physical IMSIC block. Physically, the guest-file (G-file) assigned to
this vCPU lives at a hart-relative offset given by guest_file_id (assigned
via the vGEIN allocator). Therefore, imsic_map_guest_file() uses stage-2
translation to redirect the guest's fixed per-vCPU GPA page (offset 0) to
the specific physical guest-file page.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
Changes in v2:
 - Use GUEST_IMSIC_S_BASE instead of imsic_cfg.base_addr as the base of the
   guest address to map to, and change the type of gaddr to paddr_t as it
   holds a guest physical address.
 - Rename guest_stride to guest_offset: it is an offset of the VS-file inside
   the pCPU's IMSIC block, not a stride.
 - Use PRIpaddr for physical addresses and %u for unsigned values in the
   debug/error messages.
 - Switch the mapping failure message from printk() to dprintk(XENLOG_ERR, ...).
 - Update the comment above imsic_map_guest_file(): vCPUs aren't pinned, they
   run on the pCPU chosen by the scheduler, and mention that on migration a
   VS-file is acquired on the new pCPU and mapped at the same GFN, so the
   stale mapping is replaced rather than explicitly torn down.
---
---
 xen/arch/riscv/imsic.c | 66 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 65 insertions(+), 1 deletion(-)

diff --git a/xen/arch/riscv/imsic.c b/xen/arch/riscv/imsic.c
index 07152066116a..374a21ace15f 100644
--- a/xen/arch/riscv/imsic.c
+++ b/xen/arch/riscv/imsic.c
@@ -29,6 +29,7 @@
 #include <asm/aia.h>
 #include <asm/aplic.h>
 #include <asm/imsic.h>
+#include <asm/p2m.h>
 
 #define IMSIC_HART_SIZE(guest_bits) (BIT(guest_bits, U) * IMSIC_MMIO_PAGE_SZ)
 
@@ -537,9 +538,72 @@ void cf_check imsic_ctxt_switch_to(struct vcpu *v)
     read_unlock_irqrestore(&imsic_state->vsfile_lock, flags);
 }
 
+/*
+ * Map the physical IMSIC guest interrupt file (G-file) assigned to vCPU
+ * into the domain's stage-2 guest-physical address space.
+ *
+ * In the machine's physical address space (SPA), each hart's IMSIC
+ * supervisor-level file (S-file) is located at offset 0 of its address block,
+ * followed contiguously by GEILEN guest files at offsets of 1, 2, ..., N 
pages.
+ *
+ * Because a guest OS running in VS-mode expects its own supervisor-level
+ * interrupt file to be at offset 0 of its guest-physical IMSIC block, the
+ * hypervisor must use stage-2 address translation to map the vCPU's
+ * guest-physical "supervisor" page (GPA offset 0) to the specific
+ * physical guest file page (SPA offset guest_file_id) on the physical hart.
+ *
+ * A vCPU runs on the pCPU the scheduler picked for it (v->processor), and
+ * the guest file it is given (guest_file_id, from the vGEIN allocator)
+ * belongs to that very pCPU's IMSIC. A guest_file_id of 0 indicates that no
+ * hardware guest file is selected (matching the architectural behavior where
+ * vGEIN = 0 in the hstatus CSR selects no guest external interrupt source),
+ * requiring the VS-file to be emulated in software.
+ *
+ * Consequently the mapping installed here is only valid as long as the vCPU
+ * stays on that pCPU. When it migrates, a VS-file is acquired on the new
+ * pCPU and mapped at the very same GFN, so the stale mapping needs no
+ * explicit tear-down: it is simply replaced.
+ *
+ * The base guest-physical address advertised to the guest in the device
+ * tree matches offset 0 of the vCPU's virtual IMSIC block. Stage-2
+ * translation ensures that guest supervisor accesses to this page are
+ * transparently routed to the real hardware VS-file granted to it on
+ * the pCPU it currently runs on.
+ */
 int imsic_map_guest_file(struct vcpu *v, unsigned int vsfile_id)
 {
-    return -EOPNOTSUPP;
+    struct domain *d = v->domain;
+    unsigned int cpu = v->processor;
+    paddr_t gaddr = GUEST_IMSIC_S_BASE + (IMSIC_MMIO_PAGE_SZ * v->vcpu_id);
+    paddr_t paddr, guest_offset;
+    int res;
+
+    /* Nothing to map in the case of sw interrupt file. */
+    if ( !vsfile_id )
+        return 0;
+
+    guest_offset = vsfile_id * IMSIC_MMIO_PAGE_SZ;
+
+    paddr = imsic_cfg.msi[cpu].base_addr + imsic_cfg.msi[cpu].offset +
+            guest_offset;
+
+#ifdef IMSIC_DEBUG
+    printk(XENLOG_DEBUG
+           "%s: %pv: ga(%#"PRIpaddr") -> pa(%#"PRIpaddr"), cpu(%u), "
+           "guest_file_id(%u) base_addr(%#"PRIpaddr") offset(%#lx)\n",
+           __func__, v, gaddr, paddr, cpu, vsfile_id,
+           imsic_cfg.msi[cpu].base_addr, imsic_cfg.msi[cpu].offset);
+#endif
+
+    res = map_regions_p2mt(d, gaddr_to_gfn(gaddr),
+                           PFN_DOWN(IMSIC_MMIO_PAGE_SZ), maddr_to_mfn(paddr),
+                           arch_dt_passthrough_p2m_type());
+    if ( res )
+        dprintk(XENLOG_ERR,
+                "%s: Failed to map %#"PRIpaddr" to the guest at 
%#"PRIpaddr"\n",
+                __func__, paddr, gaddr);
+
+    return res;
 }
 
 int cf_check vcpu_imsic_init(struct vcpu *v)
-- 
2.55.0