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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@citrix.com> Signed-off-by: Jan Beulich <jbeulich@suse.com> Tested-by: Paul Durrant <Paul.Durrant@citrix.com> Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
This commit is contained in:
Jan Beulich committed
1 parent
7f679c4fed
commit
5ec164fd61
1 file changed
+62
-41
+62
-41
@@ -26,46 +26,6 @@
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get_edd:
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cmpb $2, bootsym(opt_edd) # edd=off ?
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je edd_done
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cmpb $1, bootsym(opt_edd) # edd=skipmbr ?
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je edd_start
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# Read the first sector of each BIOS disk device and store the 4-byte signature
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edd_mbr_sig_start:
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movb $0x80, %dl # from device 80
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movw $bootsym(boot_mbr_signature),%bx # store buffer ptr in bx
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edd_mbr_sig_read:
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pushw %bx
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movb $0x02, %ah # 0x02 Read Sectors
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movb $1, %al # read 1 sector
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movb $0, %dh # at head 0
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movw $1, %cx # cylinder 0, sector 0
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pushw %es
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pushw %ds
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popw %es
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movw $bootsym(boot_edd_info), %bx # disk's data goes into info
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pushw %dx # work around buggy BIOSes
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stc # work around buggy BIOSes
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int $0x13
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sti # work around buggy BIOSes
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popw %dx
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popw %es
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popw %bx
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jc edd_mbr_sig_done # on failure, we're done.
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cmpb $0, %ah # some BIOSes do not set CF
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jne edd_mbr_sig_done # on failure, we're done.
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cmpw $0xaa55, bootsym(boot_edd_info)+0x1fe
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jne .Ledd_mbr_sig_next
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movl bootsym(boot_edd_info)+EDD_MBR_SIG_OFFSET,%eax
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movb %dl, (%bx) # store BIOS drive number
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movl %eax, 4(%bx) # store signature from MBR
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incb bootsym(boot_mbr_signature_nr) # note that we stored something
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addw $8, %bx # increment sig buffer ptr
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.Ledd_mbr_sig_next:
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incb %dl # increment to next device
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jz edd_mbr_sig_done
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cmpb $EDD_MBR_SIG_MAX,bootsym(boot_mbr_signature_nr)
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jb edd_mbr_sig_read
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edd_mbr_sig_done:
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# Do the BIOS Enhanced Disk Drive calls
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# This consists of two calls:
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@@ -136,10 +96,71 @@ edd_legacy_done:
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edd_next:
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incb %dl # increment to next device
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jz edd_done
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cmpb $EDD_INFO_MAX,bootsym(boot_edd_info_nr)
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jb edd_check_ext
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edd_done:
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cmpb $1, bootsym(opt_edd) # edd=skipmbr ?
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je .Ledd_mbr_sig_skip
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# Read the first sector of each BIOS disk device and store the 4-byte signature
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.Ledd_mbr_sig_start:
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pushw %es
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movb $0x80, %dl # from device 80
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movw $bootsym(boot_mbr_signature), %bx # store buffer ptr in bx
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.Ledd_mbr_sig_read:
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pushw %bx
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movw $bootsym(boot_edd_info), %bx
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movzbw bootsym(boot_edd_info_nr), %cx
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jcxz .Ledd_mbr_sig_default
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.Ledd_mbr_sig_find_info:
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cmpb %dl, (%bx)
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ja .Ledd_mbr_sig_default
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je .Ledd_mbr_sig_get_size
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add $EDDEXTSIZE+EDDPARMSIZE, %bx
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loop .Ledd_mbr_sig_find_info
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.Ledd_mbr_sig_default:
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movw $(512 >> 4), %bx
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jmp .Ledd_mbr_sig_set_buf
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.Ledd_mbr_sig_get_size:
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movw EDDEXTSIZE+0x18(%bx), %bx # sector size
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shr $4, %bx # convert to paragraphs
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jz .Ledd_mbr_sig_default
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.Ledd_mbr_sig_set_buf:
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movw %ds, %ax
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subw %bx, %ax # disk's data goes right ahead
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movw %ax, %es # of trampoline
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xorw %bx, %bx
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movw %bx, %es:0x1fe(%bx) # clear BIOS magic just in case
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pushw %dx # work around buggy BIOSes
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stc # work around buggy BIOSes
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movw $0x0201, %ax # read 1 sector
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movb $0, %dh # at head 0
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movw $1, %cx # cylinder 0, sector 0
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int $0x13
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sti # work around buggy BIOSes
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popw %dx
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movw %es:0x1fe(%bx), %si
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movl %es:EDD_MBR_SIG_OFFSET(%bx), %ecx
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popw %bx
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jc .Ledd_mbr_sig_done # on failure, we're done.
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testb %ah, %ah # some BIOSes do not set CF
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jnz .Ledd_mbr_sig_done # on failure, we're done.
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cmpw $0xaa55, %si
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jne .Ledd_mbr_sig_next
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movb %dl, (%bx) # store BIOS drive number
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movl %ecx, 4(%bx) # store signature from MBR
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incb bootsym(boot_mbr_signature_nr) # note that we stored something
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addw $8, %bx # increment sig buffer ptr
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.Ledd_mbr_sig_next:
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incb %dl # increment to next device
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jz .Ledd_mbr_sig_done
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cmpb $EDD_MBR_SIG_MAX, bootsym(boot_mbr_signature_nr)
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jb .Ledd_mbr_sig_read
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.Ledd_mbr_sig_done:
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popw %es
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.Ledd_mbr_sig_skip:
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ret
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GLOBAL(boot_edd_info_nr)
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@@ -149,4 +170,4 @@ GLOBAL(boot_mbr_signature_nr)
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GLOBAL(boot_mbr_signature)
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.fill EDD_MBR_SIG_MAX*8,1,0
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GLOBAL(boot_edd_info)
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.fill 512,1,0 # big enough for a disc sector
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.fill EDD_INFO_MAX * (EDDEXTSIZE + EDDPARMSIZE), 1, 0
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