Put PRAMIN-pointer and BAR2-page-table-PRAMIN-pointer logic into bus.c

Derived from logic in `runlist.c` and `mmu.c`. The new functions
are not directly used in this commit.

3 files changed, 134 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index 2e588fa..c2d2e96 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 obj-m += nvdebug.o
 nvdebug-objs = runlist_procfs.o device_info_procfs.o runlist.o mmu.o \
-               nvdebug_entry.o copy_topology_procfs.o
+               nvdebug_entry.o bus.o copy_topology_procfs.o
 KBUILD_CFLAGS += -DGIT_HASH=\"$(shell git --git-dir=$(PWD)/.git rev-parse --short HEAD)\"
 # -mfentry above if not building due to mcount missing
 
diff --git a/bus.c b/bus.c
new file mode 100644
index 0000000..802b6df
--- /dev/null
+++ b/bus.c
@@ -0,0 +1,130 @@
+/* Copyright 2024 Joshua Bakita
+ * Helpers for dealing with the PCIe and platform bus
+ *
+ * = Design Notes =
+ * We have to use PRAMIN to access the BAR2 page table. While it's typically also
+ * mapped into BAR2, we have no way to know where without the table. If the table
+ * changes, the new sections will have new mappings in BAR2, repeating the
+ * problem, and making caching insufficient.
+ *
+ * = Terms =
+ * VRAM/VID_MEM: Video RAM; Addresses to physical frames in the on-GPU RAM.
+ * SYS_MEM: System Memory; "Bus addresses"; Addresses which can be presented to
+ *          the PCIe Host for resolution. On x86_64 without an IOMMU, these are
+ *          just physical addresses, but may be I/O Virtual Addresses (IOVAs)
+ *          or translated via an I/O MMU on other platforms; DMA Addresses.
+ * PEER: Addresses to RAM on another GPU.
+ */
+#include <linux/printk.h> // For printk()
+#include <asm/errno.h> // For error defines
+#include <asm/io.h> // For readl()
+
+#include "nvdebug.h"
+
+/* Obtain the PRAMIN offset at which `addr` can be accessed
+  @param addr   Address to find
+  @param target Which address space to use (VRAM, SYS_MEM, PEER(?))
+  @return positive offset or -EINVAL on invalid arguments
+
+  Note: Will move the PRAMIN window to accomodate the request. Only guarantees
+        that the surrounding 64KiB window will be accessible.
+  Note: Moving the PRAMIN window will cause problems if it races with driver
+        code that tries to do the same, or expects the window not to move.
+  Bugs: Untested on PEER.
+*/
+int addr_to_pramin_mut(struct nvdebug_state *g,
+                       uint64_t addr, enum INST_TARGET target) {
+        bar0_window_t window;
+        uint64_t pramin_base;
+        // For us, accuracy and robustness is more important than speed
+        // Check that the address is valid (49 bits are addressable on-GPU, but
+        // PRAMIN only supports up to 40 bits).
+        if (addr & ~0x000000ffffffffff) {
+                printk(KERN_ERR "[nvdebug] Invalid address %llx passed to %s!\n",
+                       addr, __func__);
+                return -EINVAL;
+        }
+        window.raw = nvdebug_readl(g, NV_PBUS_BAR0_WINDOW);
+        if (window.target != target)
+                goto relocate;
+        pramin_base = ((uint64_t)window.base) << 16;
+        if (addr < pramin_base || addr > pramin_base + NV_PRAMIN_LEN)
+                goto relocate;
+        return addr - pramin_base; // Guaranteed to be < 1MiB, so safe for int
+relocate:
+        printk(KERN_INFO "[nvdebug] Moving PRAMIN win from base %llx to %llx to accomodate %#018llx\n", pramin_base, (addr >> 16) << 16, addr);
+        // Move PRAMIN window to a 64KiB-aligned address
+        window.base = (u32)(addr >> 16); // Safe, due to above range check
+        window.target = target;
+        nvdebug_writel(g, NV_PBUS_BAR0_WINDOW, window.raw);
+        return (int)(addr & 0xffffull);
+}
+
+
+/* Get a persistent pointer to the page directory base
+  @param pdb Dereferencable pointer to the zeroeth entry of top-level page
+             directory (PD3) for the BAR2 register region.
+  Note: The returned pointer will be into the PRAMIN space. If the PRAMIN
+        window is moved to a region that does not cover the BAR2 page table,
+        this ***will move the window***.
+  Note: Even if the page table is located in SYS_MEM, we route reads/writes via
+        PRAMIN. This ensures that we always see what the GPU sees, and that
+        includes any passes through I/O MMUs or IOVA spaces.
+*/
+int get_bar2_pdb(struct nvdebug_state *g, void **pdb, bool *is_v2_pdb) {
+        static void* cached_pdb = NULL;
+        static bool cached_is_v2_pdb = false;
+        static long pd_hash = 0;
+        int ret;
+        bar_config_block_t bar2_block;
+        page_dir_config_t pd_config;
+        uint64_t pdb_vram;
+
+        // Use cached base as long as it's still pointing to the same thing
+        if (cached_pdb && readl(cached_pdb) == pd_hash) {
+                *pdb = cached_pdb;
+                *is_v2_pdb = cached_is_v2_pdb;
+                return 0;
+        }
+
+        if (!g->bar2)
+                return -ENXIO;
+
+        // BAR2 has its own instance block (typically in VRAM) which contains the
+        // Page Directory Base (PDB), a pointer to a page directory/table
+        // hierarchy used to translate BAR2 offsets to VRAM or SYS_MEM addresses.
+
+        // Determine location of BAR2 instance block
+        if ((bar2_block.raw = nvdebug_readl(g, NV_PBUS_BAR2_BLOCK)) == -1) {
+                printk(KERN_ERR "[nvdebug] Unable to read BAR2/3 configuration! BAR2/3 inaccessible.\n");
+                return -ENOTSUPP;
+        }
+        printk(KERN_INFO "[nvdebug] BAR2 inst block @ %llx in %s's %s address space.\n", ((u64)bar2_block.ptr) << 12, target_to_text(bar2_block.target), bar2_block.is_virtual ? "virtual" : "physical");
+        // Setup PRAMIN to point at the BAR2 instance block
+        if ((ret = addr_to_pramin_mut(g, (uint64_t)bar2_block.ptr << 12, bar2_block.target)) < 0) {
+                printk(KERN_ERR "[nvdebug] Invalid BAR2/3 Instance Block configuration! BAR2/3 inaccessible.\n");
+                return ret;
+        }
+        printk(KERN_INFO "[nvdebug] BAR2 inst block at off %x in PRAMIN\n", ret);
+        // Pull the page directory base configuration from the instance block
+        if ((pd_config.raw = nvdebug_readq(g, NV_PRAMIN + ret + NV_PRAMIN_PDB_CONFIG_OFF)) == -1) {
+                printk(KERN_ERR "[nvdebug] Unable to read BAR2/3 PDB configuration! BAR2/3 inaccessible.\n");
+                return -ENOTSUPP;
+        }
+        pdb_vram = pd_config.page_dir_hi;
+        pdb_vram <<= 20;
+        pdb_vram |= pd_config.page_dir_lo;
+        pdb_vram <<= 12;
+        printk(KERN_INFO "[nvdebug] BAR2 PDB @ %llx (config raw: %llx)\n", pdb_vram, pd_config.raw);
+        // Setup PRAMIN to point at the page directory
+        if ((ret = addr_to_pramin_mut(g, pdb_vram, pd_config.target)) < 0) {
+                printk(KERN_ERR "[nvdebug] Invalid BAR2/3 PDB configuration! BAR2/3 inaccessible.\n");
+                return ret;
+        }
+
+        *pdb = cached_pdb = g->regs + NV_PRAMIN + ret;
+        pd_hash = readl(cached_pdb);
+        *is_v2_pdb = cached_is_v2_pdb = pd_config.is_ver2;
+
+        return 0;
+}
diff --git a/nvdebug.h b/nvdebug.h
index ac254f0..2fc8c63 100644
--- a/nvdebug.h
+++ b/nvdebug.h
@@ -1141,3 +1141,6 @@ static inline void nvdebug_writeq(struct nvdebug_state *s, u32 r, u64 v) {
         writeq_relaxed(v, s->regs + r);
         wmb();
 }
+// Defined in bus.c
+int addr_to_pramin_mut(struct nvdebug_state *g, uint64_t addr, enum INST_TARGET target);
+int get_bar2_pdb(struct nvdebug_state *g, void **pdb, bool *is_v2_pdb);