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Re: [Xen-devel] [RFC v2 0/4] QEMU changes to do PVH boot



Hi Stefano,

On 10/01/2019 15:12, Stefano Garzarella wrote:
On Wed, Jan 09, 2019 at 01:18:12PM -0800, Maran Wilson wrote:
On 1/9/2019 11:53 AM, Boris Ostrovsky wrote:
On 1/9/19 6:53 AM, Stefano Garzarella wrote:
Hi Liam,

On Tue, Jan 8, 2019 at 3:47 PM Liam Merwick <liam.merwick@xxxxxxxxxx> wrote:
QEMU sets the hvm_modlist_entry in load_linux() after the call to
load_elfboot() and then qboot loads it in boot_pvh_from_fw_cfg()

But the current PVH patches don't handle initrd (they have
start_info.nr_modules == 1).
Looking in the linux kernel (arch/x86/platform/pvh/enlighten.c) I saw:
      /* The first module is always ramdisk. */
      if (pvh_start_info.nr_modules) {
          struct hvm_modlist_entry *modaddr =
              __va(pvh_start_info.modlist_paddr);
          pvh_bootparams.hdr.ramdisk_image = modaddr->paddr;
          pvh_bootparams.hdr.ramdisk_size = modaddr->size;
      }

So, putting start_info.nr_modules = 1, means that the first
hvm_modlist_entry should have the ramdisk paddr and size. Is it
correct?

That's my understanding.

I think what's missing, is that we just need Qemu or qboot/seabios to
properly populate the pvh_start_info.modlist_paddr with the address (as
usable by the guest) of the hvm_modlist_entry which correctly defines the
details of the initrd that has already been loaded into memory that is
accessible by the guest.

-Maran


I tried and it works, I modified QEMU to load the initrd and to expose it
through fw_cfg, then qboot loads it and set correctly the hvm_modlist_entry.

You can find the patch of QEMU at the end of this email and the qboot
patch here: 
https://github.com/stefano-garzarella/qboot/commit/41e1fd765c8419e270fd79d9b3af5d53576e88a8

Do you think can be a good approach? If you want, you can add this patch
to your series.

Code looks good to me. I'll include it with v3 of my QEMU patches.

Regards,
Liam



Thanks,
Stefano


 From d5c0d51768f5a8fb214be6c2bb0cb7e86e9917b7 Mon Sep 17 00:00:00 2001
From: Stefano Garzarella <sgarzare@xxxxxxxxxx>
Date: Thu, 10 Jan 2019 15:16:44 +0100
Subject: [PATCH] pvh: load initrd and expose it through fw_cfg

When initrd is specified, load and expose it to the guest firmware
through fw_cfg. The firmware will fill the hvm_start_info for the
kernel.

Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
Based-on: <1545422632-24444-5-git-send-email-liam.merwick@xxxxxxxxxx>
---
  hw/i386/pc.c | 38 +++++++++++++++++++++++++++++---------
  1 file changed, 29 insertions(+), 9 deletions(-)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 06bce6a101..f6721f51be 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -986,25 +986,45 @@ static void load_linux(PCMachineState *pcms,
           */
          if (load_elfboot(kernel_filename, kernel_size,
                           header, pvh_start_addr, fw_cfg)) {
-            struct hvm_modlist_entry ramdisk_mod = { 0 };
-
              fclose(f);
fw_cfg_add_i32(fw_cfg, FW_CFG_CMDLINE_SIZE,
                  strlen(kernel_cmdline) + 1);
              fw_cfg_add_string(fw_cfg, FW_CFG_CMDLINE_DATA, kernel_cmdline);
- assert(machine->device_memory != NULL);
-            ramdisk_mod.paddr = machine->device_memory->base;
-            ramdisk_mod.size =
-                memory_region_size(&machine->device_memory->mr);
-
-            fw_cfg_add_bytes(fw_cfg, FW_CFG_KERNEL_DATA, &ramdisk_mod,
-                             sizeof(ramdisk_mod));
              fw_cfg_add_i32(fw_cfg, FW_CFG_SETUP_SIZE, sizeof(header));
              fw_cfg_add_bytes(fw_cfg, FW_CFG_SETUP_DATA,
                               header, sizeof(header));
+ /* load initrd */
+            if (initrd_filename) {
+                gsize initrd_size;
+                gchar *initrd_data;
+                GError *gerr = NULL;
+
+                if (!g_file_get_contents(initrd_filename, &initrd_data,
+                            &initrd_size, &gerr)) {
+                    fprintf(stderr, "qemu: error reading initrd %s: %s\n",
+                            initrd_filename, gerr->message);
+                    exit(1);
+                }
+
+                initrd_max = pcms->below_4g_mem_size - pcmc->acpi_data_size - 
1;
+                if (initrd_size >= initrd_max) {
+                    fprintf(stderr, "qemu: initrd is too large, cannot 
support."
+                            "(max: %"PRIu32", need %"PRId64")\n",
+                            initrd_max, (uint64_t)initrd_size);
+                    exit(1);
+                }
+
+                initrd_addr = (initrd_max - initrd_size) & ~4095;
+
+                fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_ADDR, initrd_addr);
+                fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_SIZE, initrd_size);
+                fw_cfg_add_bytes(fw_cfg, FW_CFG_INITRD_DATA, initrd_data,
+                                 initrd_size);
+            }
+
              return;
          }
          /* This looks like a multiboot kernel. If it is, let's stop


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