[PULL,04/15] RISC-V: Copy the fdt in dram instead of ROM

Commit Message

Alistair Francis July 14, 2020, 12:32 a.m. UTC

From: Atish Patra <[e-mail]>

Currently, the fdt is copied to the ROM after the reset vector. The firmware
has to copy it to DRAM. Instead of this, directly copy the device tree to a
pre-computed dram address. The device tree load address should be as far as
possible from kernel and initrd images. That's why it is kept at the end of
the DRAM or 4GB whichever is lesser.

Signed-off-by: Atish Patra <[e-mail]>
Reviewed-by: Alistair Francis <[e-mail]>
Reviewed-by: Bin Meng <[e-mail]>
Tested-by: Bin Meng <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Alistair Francis <[e-mail]>
---
 include/hw/riscv/boot.h |  4 +++-
 hw/riscv/boot.c         | 53 +++++++++++++++++++++++++++++------------
 hw/riscv/sifive_u.c     | 28 ++++++++++------------
 hw/riscv/spike.c        |  7 +++++-
 hw/riscv/virt.c         |  7 +++++-
 5 files changed, 66 insertions(+), 33 deletions(-)

Comments

Peter Maydell July 13, 2021, 10:43 a.m. UTC | #1

On Tue, 14 Jul 2020 at 01:44, Alistair Francis <[e-mail]> wrote:
>
> From: Atish Patra <[e-mail]>
>
> Currently, the fdt is copied to the ROM after the reset vector. The firmware
> has to copy it to DRAM. Instead of this, directly copy the device tree to a
> pre-computed dram address. The device tree load address should be as far as
> possible from kernel and initrd images. That's why it is kept at the end of
> the DRAM or 4GB whichever is lesser.

Hi; Coverity reports an issue in this code (CID 1458136):

> +uint32_t riscv_load_fdt(hwaddr dram_base, uint64_t mem_size, void *fdt)
> +{
> +    uint32_t temp, fdt_addr;
> +    hwaddr dram_end = dram_base + mem_size;
> +    int fdtsize = fdt_totalsize(fdt);
> +
> +    if (fdtsize <= 0) {
> +        error_report("invalid device-tree");
> +        exit(1);
> +    }
> +
> +    /*
> +     * We should put fdt as far as possible to avoid kernel/initrd overwriting
> +     * its content. But it should be addressable by 32 bit system as well.
> +     * Thus, put it at an aligned address that less than fdt size from end of
> +     * dram or 4GB whichever is lesser.
> +     */
> +    temp = MIN(dram_end, 4096 * MiB);
> +    fdt_addr = QEMU_ALIGN_DOWN(temp - fdtsize, 2 * MiB);
> +
> +    fdt_pack(fdt);

fdt_pack() can return an error code, but we are not checking its
return value here.

(This is one of Coverity's heuristics where it only reports failure
to check errors if it sees enough other callsites in the codebase
which do check errors to make it decide this is an "always need a
check" API, which is why the error has only popped up now a year on...)

> +    /* copy in the device tree */
> +    qemu_fdt_dumpdtb(fdt, fdtsize);
> +
> +    rom_add_blob_fixed_as("fdt", fdt, fdtsize, fdt_addr,
> +                          &address_space_memory);
> +
> +    return fdt_addr;
> +}

thanks
-- PMM

Alistair Francis July 14, 2021, 6:35 a.m. UTC | #2

On Tue, Jul 13, 2021 at 8:44 PM Peter Maydell <[e-mail]> wrote:
>
> On Tue, 14 Jul 2020 at 01:44, Alistair Francis <[e-mail]> wrote:
> >
> > From: Atish Patra <[e-mail]>
> >
> > Currently, the fdt is copied to the ROM after the reset vector. The firmware
> > has to copy it to DRAM. Instead of this, directly copy the device tree to a
> > pre-computed dram address. The device tree load address should be as far as
> > possible from kernel and initrd images. That's why it is kept at the end of
> > the DRAM or 4GB whichever is lesser.
>
> Hi; Coverity reports an issue in this code (CID 1458136):
>
> > +uint32_t riscv_load_fdt(hwaddr dram_base, uint64_t mem_size, void *fdt)
> > +{
> > +    uint32_t temp, fdt_addr;
> > +    hwaddr dram_end = dram_base + mem_size;
> > +    int fdtsize = fdt_totalsize(fdt);
> > +
> > +    if (fdtsize <= 0) {
> > +        error_report("invalid device-tree");
> > +        exit(1);
> > +    }
> > +
> > +    /*
> > +     * We should put fdt as far as possible to avoid kernel/initrd overwriting
> > +     * its content. But it should be addressable by 32 bit system as well.
> > +     * Thus, put it at an aligned address that less than fdt size from end of
> > +     * dram or 4GB whichever is lesser.
> > +     */
> > +    temp = MIN(dram_end, 4096 * MiB);
> > +    fdt_addr = QEMU_ALIGN_DOWN(temp - fdtsize, 2 * MiB);
> > +
> > +    fdt_pack(fdt);
>
> fdt_pack() can return an error code, but we are not checking its
> return value here.
>
> (This is one of Coverity's heuristics where it only reports failure
> to check errors if it sees enough other callsites in the codebase
> which do check errors to make it decide this is an "always need a
> check" API, which is why the error has only popped up now a year on...)

Thanks Peter, sending a patch now.

Alistair

>
> > +    /* copy in the device tree */
> > +    qemu_fdt_dumpdtb(fdt, fdtsize);
> > +
> > +    rom_add_blob_fixed_as("fdt", fdt, fdtsize, fdt_addr,
> > +                          &address_space_memory);
> > +
> > +    return fdt_addr;
> > +}
>
> thanks
> -- PMM
>

Patch

diff --git a/include/hw/riscv/boot.h b/include/hw/riscv/boot.h
index 3e9759c89a..35b6ddf710 100644
--- a/include/hw/riscv/boot.h
+++ b/include/hw/riscv/boot.h
@@ -35,7 +35,9 @@  target_ulong riscv_load_kernel(const char *kernel_filename,
                                symbol_fn_t sym_cb);
 hwaddr riscv_load_initrd(const char *filename, uint64_t mem_size,
                          uint64_t kernel_entry, hwaddr *start);
+uint32_t riscv_load_fdt(hwaddr dram_start, uint64_t dram_size, void *fdt);
 void riscv_setup_rom_reset_vec(hwaddr saddr, hwaddr rom_base,
-                               hwaddr rom_size, void *fdt);
+                               hwaddr rom_size,
+                               uint32_t fdt_load_addr, void *fdt);
 
 #endif /* RISCV_BOOT_H */
diff --git a/hw/riscv/boot.c b/hw/riscv/boot.c
index 3df802380a..c62f545f15 100644
--- a/hw/riscv/boot.c
+++ b/hw/riscv/boot.c
@@ -159,45 +159,68 @@  hwaddr riscv_load_initrd(const char *filename, uint64_t mem_size,
     return *start + size;
 }
 
+uint32_t riscv_load_fdt(hwaddr dram_base, uint64_t mem_size, void *fdt)
+{
+    uint32_t temp, fdt_addr;
+    hwaddr dram_end = dram_base + mem_size;
+    int fdtsize = fdt_totalsize(fdt);
+
+    if (fdtsize <= 0) {
+        error_report("invalid device-tree");
+        exit(1);
+    }
+
+    /*
+     * We should put fdt as far as possible to avoid kernel/initrd overwriting
+     * its content. But it should be addressable by 32 bit system as well.
+     * Thus, put it at an aligned address that less than fdt size from end of
+     * dram or 4GB whichever is lesser.
+     */
+    temp = MIN(dram_end, 4096 * MiB);
+    fdt_addr = QEMU_ALIGN_DOWN(temp - fdtsize, 2 * MiB);
+
+    fdt_pack(fdt);
+    /* copy in the device tree */
+    qemu_fdt_dumpdtb(fdt, fdtsize);
+
+    rom_add_blob_fixed_as("fdt", fdt, fdtsize, fdt_addr,
+                          &address_space_memory);
+
+    return fdt_addr;
+}
+
 void riscv_setup_rom_reset_vec(hwaddr start_addr, hwaddr rom_base,
-                               hwaddr rom_size, void *fdt)
+                               hwaddr rom_size,
+                               uint32_t fdt_load_addr, void *fdt)
 {
     int i;
 
     /* reset vector */
-    uint32_t reset_vec[8] = {
+    uint32_t reset_vec[10] = {
         0x00000297,                  /* 1:  auipc  t0, %pcrel_hi(dtb) */
-        0x02028593,                  /*     addi   a1, t0, %pcrel_lo(1b) */
         0xf1402573,                  /*     csrr   a0, mhartid  */
 #if defined(TARGET_RISCV32)
+        0x0202a583,                  /*     lw     a1, 32(t0) */
         0x0182a283,                  /*     lw     t0, 24(t0) */
 #elif defined(TARGET_RISCV64)
+        0x0202b583,                  /*     ld     a1, 32(t0) */
         0x0182b283,                  /*     ld     t0, 24(t0) */
 #endif
         0x00028067,                  /*     jr     t0 */
         0x00000000,
         start_addr,                  /* start: .dword */
+        0x00000000,
+        fdt_load_addr,               /* fdt_laddr: .dword */
         0x00000000,
                                      /* dtb: */
     };
 
     /* copy in the reset vector in little_endian byte order */
-    for (i = 0; i < sizeof(reset_vec) >> 2; i++) {
+    for (i = 0; i < ARRAY_SIZE(reset_vec); i++) {
         reset_vec[i] = cpu_to_le32(reset_vec[i]);
     }
     rom_add_blob_fixed_as("mrom.reset", reset_vec, sizeof(reset_vec),
                           rom_base, &address_space_memory);
 
-    /* copy in the device tree */
-    if (fdt_pack(fdt) || fdt_totalsize(fdt) >
-        rom_size - sizeof(reset_vec)) {
-        error_report("not enough space to store device-tree");
-        exit(1);
-    }
-    qemu_fdt_dumpdtb(fdt, fdt_totalsize(fdt));
-    rom_add_blob_fixed_as("mrom.fdt", fdt, fdt_totalsize(fdt),
-                           rom_base + sizeof(reset_vec),
-                           &address_space_memory);
-
     return;
 }
diff --git a/hw/riscv/sifive_u.c b/hw/riscv/sifive_u.c
index 0695c93d2c..39923209f4 100644
--- a/hw/riscv/sifive_u.c
+++ b/hw/riscv/sifive_u.c
@@ -379,6 +379,7 @@  static void sifive_u_machine_init(MachineState *machine)
     MemoryRegion *flash0 = g_new(MemoryRegion, 1);
     target_ulong start_addr = memmap[SIFIVE_U_DRAM].base;
     int i;
+    uint32_t fdt_load_addr;
 
     /* Initialize SoC */
     object_initialize_child(OBJECT(machine), "soc", &s->soc, TYPE_RISCV_U_SOC);
@@ -450,40 +451,37 @@  static void sifive_u_machine_init(MachineState *machine)
         }
     }
 
+    /* Compute the fdt load address in dram */
+    fdt_load_addr = riscv_load_fdt(memmap[SIFIVE_U_DRAM].base,
+                                   machine->ram_size, s->fdt);
+
     /* reset vector */
-    uint32_t reset_vec[8] = {
+    uint32_t reset_vec[11] = {
         s->msel,                       /* MSEL pin state */
         0x00000297,                    /* 1:  auipc  t0, %pcrel_hi(dtb) */
-        0x01c28593,                    /*     addi   a1, t0, %pcrel_lo(1b) */
         0xf1402573,                    /*     csrr   a0, mhartid  */
 #if defined(TARGET_RISCV32)
+        0x0202a583,                    /*     lw     a1, 32(t0) */
         0x0182a283,                    /*     lw     t0, 24(t0) */
 #elif defined(TARGET_RISCV64)
-        0x0182e283,                    /*     lwu    t0, 24(t0) */
+        0x0202b583,                    /*     ld     a1, 32(t0) */
+        0x0182b283,                    /*     ld     t0, 24(t0) */
 #endif
         0x00028067,                    /*     jr     t0 */
         0x00000000,
         start_addr,                    /* start: .dword */
+        0x00000000,
+        fdt_load_addr,                 /* fdt_laddr: .dword */
+        0x00000000,
                                        /* dtb: */
     };
 
     /* copy in the reset vector in little_endian byte order */
-    for (i = 0; i < sizeof(reset_vec) >> 2; i++) {
+    for (i = 0; i < ARRAY_SIZE(reset_vec); i++) {
         reset_vec[i] = cpu_to_le32(reset_vec[i]);
     }
     rom_add_blob_fixed_as("mrom.reset", reset_vec, sizeof(reset_vec),
                           memmap[SIFIVE_U_MROM].base, &address_space_memory);
-
-    /* copy in the device tree */
-    if (fdt_pack(s->fdt) || fdt_totalsize(s->fdt) >
-            memmap[SIFIVE_U_MROM].size - sizeof(reset_vec)) {
-        error_report("not enough space to store device-tree");
-        exit(1);
-    }
-    qemu_fdt_dumpdtb(s->fdt, fdt_totalsize(s->fdt));
-    rom_add_blob_fixed_as("mrom.fdt", s->fdt, fdt_totalsize(s->fdt),
-                          memmap[SIFIVE_U_MROM].base + sizeof(reset_vec),
-                          &address_space_memory);
 }
 
 static bool sifive_u_machine_get_start_in_flash(Object *obj, Error **errp)
diff --git a/hw/riscv/spike.c b/hw/riscv/spike.c
index a8a0588824..13fa0455e3 100644
--- a/hw/riscv/spike.c
+++ b/hw/riscv/spike.c
@@ -163,6 +163,7 @@  static void spike_board_init(MachineState *machine)
     MemoryRegion *main_mem = g_new(MemoryRegion, 1);
     MemoryRegion *mask_rom = g_new(MemoryRegion, 1);
     unsigned int smp_cpus = machine->smp.cpus;
+    uint32_t fdt_load_addr;
 
     /* Initialize SOC */
     object_initialize_child(OBJECT(machine), "soc", &s->soc,
@@ -208,9 +209,13 @@  static void spike_board_init(MachineState *machine)
         }
     }
 
+    /* Compute the fdt load address in dram */
+    fdt_load_addr = riscv_load_fdt(memmap[SPIKE_DRAM].base,
+                                   machine->ram_size, s->fdt);
     /* load the reset vector */
     riscv_setup_rom_reset_vec(memmap[SPIKE_DRAM].base, memmap[SPIKE_MROM].base,
-                              memmap[SPIKE_MROM].size, s->fdt);
+                              memmap[SPIKE_MROM].size,
+                              fdt_load_addr, s->fdt);
 
     /* initialize HTIF using symbols found in load_kernel */
     htif_mm_init(system_memory, mask_rom, &s->soc.harts[0].env, serial_hd(0));
diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
index 3463cf54aa..9d87319f70 100644
--- a/hw/riscv/virt.c
+++ b/hw/riscv/virt.c
@@ -478,6 +478,7 @@  static void virt_machine_init(MachineState *machine)
     char *plic_hart_config;
     size_t plic_hart_config_len;
     target_ulong start_addr = memmap[VIRT_DRAM].base;
+    uint32_t fdt_load_addr;
     int i;
     unsigned int smp_cpus = machine->smp.cpus;
 
@@ -532,9 +533,13 @@  static void virt_machine_init(MachineState *machine)
         start_addr = virt_memmap[VIRT_FLASH].base;
     }
 
+    /* Compute the fdt load address in dram */
+    fdt_load_addr = riscv_load_fdt(memmap[VIRT_DRAM].base,
+                                   machine->ram_size, s->fdt);
     /* load the reset vector */
     riscv_setup_rom_reset_vec(start_addr, virt_memmap[VIRT_MROM].base,
-                              virt_memmap[VIRT_MROM].size, s->fdt);
+                              virt_memmap[VIRT_MROM].size,
+                              fdt_load_addr, s->fdt);
 
     /* create PLIC hart topology configuration string */
     plic_hart_config_len = (strlen(VIRT_PLIC_HART_CONFIG) + 1) * smp_cpus;