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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [xen master] x86/boot: re-arrange how/when we do disk I/O
commit 5ec164fd61bd8fc7adfb1ca2907d9159eeb1e37b
Author: Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Jun 13 10:41:10 2017 +0200
Commit: Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jun 13 10:41:10 2017 +0200
x86/boot: re-arrange how/when we do disk I/O
We place the trampoline no lower than at 256k, so we have ample space
to read the MBRs of BIOS disks into an aligned buffer right below the
trampoline (not doing so has been found to be a problem on a buggy BIOS
coming with a Skull Canyon NUC). To facilitate that move MBR reading
past EDD info retrieval.
Also add a wrap check to the EDD info retrieval loop, to match that in
the MBR reading one.
Reported-by: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Tested-by: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
xen/arch/x86/boot/edd.S | 103 +++++++++++++++++++++++++++++-------------------
1 file changed, 62 insertions(+), 41 deletions(-)
diff --git a/xen/arch/x86/boot/edd.S b/xen/arch/x86/boot/edd.S
index 73371f9..3df712b 100644
--- a/xen/arch/x86/boot/edd.S
+++ b/xen/arch/x86/boot/edd.S
@@ -26,46 +26,6 @@
get_edd:
cmpb $2, bootsym(opt_edd) # edd=off ?
je edd_done
- cmpb $1, bootsym(opt_edd) # edd=skipmbr ?
- je edd_start
-
-# Read the first sector of each BIOS disk device and store the 4-byte signature
-edd_mbr_sig_start:
- movb $0x80, %dl # from device 80
- movw $bootsym(boot_mbr_signature),%bx # store buffer ptr in bx
-edd_mbr_sig_read:
- pushw %bx
- movb $0x02, %ah # 0x02 Read Sectors
- movb $1, %al # read 1 sector
- movb $0, %dh # at head 0
- movw $1, %cx # cylinder 0, sector 0
- pushw %es
- pushw %ds
- popw %es
- movw $bootsym(boot_edd_info), %bx # disk's data goes into info
- pushw %dx # work around buggy BIOSes
- stc # work around buggy BIOSes
- int $0x13
- sti # work around buggy BIOSes
- popw %dx
- popw %es
- popw %bx
- jc edd_mbr_sig_done # on failure, we're done.
- cmpb $0, %ah # some BIOSes do not set CF
- jne edd_mbr_sig_done # on failure, we're done.
- cmpw $0xaa55, bootsym(boot_edd_info)+0x1fe
- jne .Ledd_mbr_sig_next
- movl bootsym(boot_edd_info)+EDD_MBR_SIG_OFFSET,%eax
- movb %dl, (%bx) # store BIOS drive number
- movl %eax, 4(%bx) # store signature from MBR
- incb bootsym(boot_mbr_signature_nr) # note that we stored something
- addw $8, %bx # increment sig buffer ptr
-.Ledd_mbr_sig_next:
- incb %dl # increment to next device
- jz edd_mbr_sig_done
- cmpb $EDD_MBR_SIG_MAX,bootsym(boot_mbr_signature_nr)
- jb edd_mbr_sig_read
-edd_mbr_sig_done:
# Do the BIOS Enhanced Disk Drive calls
# This consists of two calls:
@@ -136,10 +96,71 @@ edd_legacy_done:
edd_next:
incb %dl # increment to next device
+ jz edd_done
cmpb $EDD_INFO_MAX,bootsym(boot_edd_info_nr)
jb edd_check_ext
edd_done:
+ cmpb $1, bootsym(opt_edd) # edd=skipmbr ?
+ je .Ledd_mbr_sig_skip
+
+# Read the first sector of each BIOS disk device and store the 4-byte signature
+.Ledd_mbr_sig_start:
+ pushw %es
+ movb $0x80, %dl # from device 80
+ movw $bootsym(boot_mbr_signature), %bx # store buffer ptr in bx
+.Ledd_mbr_sig_read:
+ pushw %bx
+ movw $bootsym(boot_edd_info), %bx
+ movzbw bootsym(boot_edd_info_nr), %cx
+ jcxz .Ledd_mbr_sig_default
+.Ledd_mbr_sig_find_info:
+ cmpb %dl, (%bx)
+ ja .Ledd_mbr_sig_default
+ je .Ledd_mbr_sig_get_size
+ add $EDDEXTSIZE+EDDPARMSIZE, %bx
+ loop .Ledd_mbr_sig_find_info
+.Ledd_mbr_sig_default:
+ movw $(512 >> 4), %bx
+ jmp .Ledd_mbr_sig_set_buf
+.Ledd_mbr_sig_get_size:
+ movw EDDEXTSIZE+0x18(%bx), %bx # sector size
+ shr $4, %bx # convert to paragraphs
+ jz .Ledd_mbr_sig_default
+.Ledd_mbr_sig_set_buf:
+ movw %ds, %ax
+ subw %bx, %ax # disk's data goes right ahead
+ movw %ax, %es # of trampoline
+ xorw %bx, %bx
+ movw %bx, %es:0x1fe(%bx) # clear BIOS magic just in case
+ pushw %dx # work around buggy BIOSes
+ stc # work around buggy BIOSes
+ movw $0x0201, %ax # read 1 sector
+ movb $0, %dh # at head 0
+ movw $1, %cx # cylinder 0, sector 0
+ int $0x13
+ sti # work around buggy BIOSes
+ popw %dx
+ movw %es:0x1fe(%bx), %si
+ movl %es:EDD_MBR_SIG_OFFSET(%bx), %ecx
+ popw %bx
+ jc .Ledd_mbr_sig_done # on failure, we're done.
+ testb %ah, %ah # some BIOSes do not set CF
+ jnz .Ledd_mbr_sig_done # on failure, we're done.
+ cmpw $0xaa55, %si
+ jne .Ledd_mbr_sig_next
+ movb %dl, (%bx) # store BIOS drive number
+ movl %ecx, 4(%bx) # store signature from MBR
+ incb bootsym(boot_mbr_signature_nr) # note that we stored something
+ addw $8, %bx # increment sig buffer ptr
+.Ledd_mbr_sig_next:
+ incb %dl # increment to next device
+ jz .Ledd_mbr_sig_done
+ cmpb $EDD_MBR_SIG_MAX, bootsym(boot_mbr_signature_nr)
+ jb .Ledd_mbr_sig_read
+.Ledd_mbr_sig_done:
+ popw %es
+.Ledd_mbr_sig_skip:
ret
GLOBAL(boot_edd_info_nr)
@@ -149,4 +170,4 @@ GLOBAL(boot_mbr_signature_nr)
GLOBAL(boot_mbr_signature)
.fill EDD_MBR_SIG_MAX*8,1,0
GLOBAL(boot_edd_info)
- .fill 512,1,0 # big enough for a disc sector
+ .fill EDD_INFO_MAX * (EDDEXTSIZE + EDDPARMSIZE), 1, 0
--
generated by git-patchbot for /home/xen/git/xen.git#master
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