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From 64fa56e0520215e3909e442f09d8073c1870648a Mon Sep 17 00:00:00 2001
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From: Thomas Huth <thuth@redhat.com>
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Date: Fri, 8 Jul 2022 20:49:01 +0200
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Subject: [PATCH 07/17] pc-bios/s390-ccw/bootmap: Improve the guessing logic in
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zipl_load_vblk()
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RH-Author: Thomas Huth <thuth@redhat.com>
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RH-MergeRequest: 106: pc-bios/s390-ccw: Fix boot from disks with 4k sectors that do not have the typical DASD geometry
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RH-Commit: [2/10] ca8f5e847617cf4ac2fd6c38edb2982f32fa3eba (thuth/qemu-kvm-cs9)
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RH-Bugzilla: 2098077
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RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
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RH-Acked-by: David Hildenbrand <david@redhat.com>
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RH-Acked-by: Cornelia Huck <cohuck@redhat.com>
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Bugzilla: http://bugzilla.redhat.com/2098077
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commit 422865f6672ee1482b98d18321b55c1ecfb06c82
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Author: Thomas Huth <thuth@redhat.com>
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Date: Mon Jul 4 13:18:54 2022 +0200
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pc-bios/s390-ccw/bootmap: Improve the guessing logic in zipl_load_vblk()
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The logic of trying an final ISO or ECKD boot on virtio-block devices is
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very weird: Since the geometry hardly ever matches in virtio_disk_is_scsi(),
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virtio_blk_setup_device() always sets a "guessed" disk geometry via
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virtio_assume_scsi() (which is certainly also wrong in a lot of cases).
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zipl_load_vblk() then sees that there's been a "virtio_guessed_disk_nature"
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and tries to fix up the geometry again via virtio_assume_iso9660() before
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always trying to do ipl_iso_el_torito(). That's a very brain-twisting
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way of attempting to boot from ISO images, which won't work anymore after
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the following patches that will clean up the virtio_assume_scsi() mess
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(and thus get rid of the "virtio_guessed_disk_nature" here).
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Let's try a better approach instead: ISO files always have a magic
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string "CD001" at offset 0x8001 (see e.g. the ECMA-119 specification)
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which we can use to decide whether we should try to boot in ISO 9660
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mode (which we should also try if we see a sector size of 2048).
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And if we were not able to boot in ISO mode here, the final boot attempt
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before panicking is to boot in ECKD mode. Since this is our last boot
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attempt anyway, simply always assume the ECKD geometry here (if the sector
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size was not 4096 yet), so that we also do not depend on the guessed disk
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geometry from virtio_blk_setup_device() here anymore.
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Message-Id: <20220704111903.62400-4-thuth@redhat.com>
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Signed-off-by: Thomas Huth <thuth@redhat.com>
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Signed-off-by: Thomas Huth <thuth@redhat.com>
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---
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pc-bios/s390-ccw/bootmap.c | 27 +++++++++++++++++++++++----
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1 file changed, 23 insertions(+), 4 deletions(-)
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diff --git a/pc-bios/s390-ccw/bootmap.c b/pc-bios/s390-ccw/bootmap.c
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index 56411ab3b6..994e59c0b0 100644
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--- a/pc-bios/s390-ccw/bootmap.c
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+++ b/pc-bios/s390-ccw/bootmap.c
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@@ -780,18 +780,37 @@ static void ipl_iso_el_torito(void)
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}
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}
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+/**
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+ * Detect whether we're trying to boot from an .ISO image.
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+ * These always have a signature string "CD001" at offset 0x8001.
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+ */
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+static bool has_iso_signature(void)
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+{
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+ int blksize = virtio_get_block_size();
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+
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+ if (!blksize || virtio_read(0x8000 / blksize, sec)) {
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+ return false;
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+ }
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+
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+ return !memcmp("CD001", &sec[1], 5);
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+}
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+
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/***********************************************************************
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* Bus specific IPL sequences
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*/
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static void zipl_load_vblk(void)
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{
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- if (virtio_guessed_disk_nature()) {
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- virtio_assume_iso9660();
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+ int blksize = virtio_get_block_size();
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+
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+ if (blksize == VIRTIO_ISO_BLOCK_SIZE || has_iso_signature()) {
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+ if (blksize != VIRTIO_ISO_BLOCK_SIZE) {
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+ virtio_assume_iso9660();
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+ }
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+ ipl_iso_el_torito();
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}
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- ipl_iso_el_torito();
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- if (virtio_guessed_disk_nature()) {
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+ if (blksize != VIRTIO_DASD_DEFAULT_BLOCK_SIZE) {
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sclp_print("Using guessed DASD geometry.\n");
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virtio_assume_eckd();
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}
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--
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2.31.1
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