| Message ID | 20130106123635.GC3440@redhat.com |
|---|---|
| State | New |
| Headers | show |
On 06.01.2013, at 13:36, Gleb Natapov wrote: > Big real mode is fully emulated by KVM now, so if control is passed to > the loaded kernel while one of the segment registers is in big real > mode all the real mode part of the Linux start up is emulated. This > slows boot process down. Fix that by resetting ES limit to 0xffff before > jumping into the kernel. > > The patch also removes unused code segment definition from GDT and changes > ES register to be 16bit in protected mode since CS stays 16bit too and > it is CS segment that determines effective operands and addresses length. > > Signed-off-by: Gleb Natapov <gleb@redhat.com> I assume you tested that things still work, so the changes look ok to me. However, this patch should also include a binary patch to pc-bios/linuxboot.bin, since linuxboot.S doesn't get compiled into the .bin form on every machine. Alex > diff --git a/pc-bios/optionrom/linuxboot.S b/pc-bios/optionrom/linuxboot.S > index 748c831..afe39a5 100644 > --- a/pc-bios/optionrom/linuxboot.S > +++ b/pc-bios/optionrom/linuxboot.S > @@ -101,18 +101,20 @@ copy_kernel: > mov $1, %eax > mov %eax, %cr0 > > - /* So we can set ES to a 32-bit segment */ > + /* So we can enlarge ES segment limit */ > mov $0x10, %eax > mov %eax, %es > > - /* We're now running in 16-bit CS, but 32-bit ES! */ > - > /* Load kernel and initrd */ > read_fw_blob_addr32(FW_CFG_KERNEL) > read_fw_blob_addr32(FW_CFG_INITRD) > read_fw_blob_addr32(FW_CFG_CMDLINE) > read_fw_blob_addr32(FW_CFG_SETUP) > > + /* Do not leave ES in big real mode */ > + mov $0x08, %eax > + mov %eax, %es > + > /* And now jump into Linux! */ > mov $0, %eax > mov %eax, %cr0 > @@ -130,10 +132,10 @@ gdt: > /* 0x00 */ > .byte 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 > > - /* 0x08: code segment (base=0, limit=0xfffff, type=32bit code exec/read, DPL=0, 4k) */ > -.byte 0xff, 0xff, 0x00, 0x00, 0x00, 0x9a, 0xcf, 0x00 > + /* 0x08: data segment (base=0, limit=0xffff, type=16bit data read/write, DPL=0, 4k) */ > +.byte 0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0x00, 0x00 > > - /* 0x10: data segment (base=0, limit=0xfffff, type=32bit data read/write, DPL=0, 4k) */ > -.byte 0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0xcf, 0x00 > + /* 0x10: data segment (base=0, limit=0xfffff, type=16bit data read/write, DPL=0, 4k) */ > +.byte 0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0x8f, 0x00 > > BOOT_ROM_END > -- > Gleb.
On Sun, Jan 06, 2013 at 01:47:17PM +0100, Alexander Graf wrote: > > On 06.01.2013, at 13:36, Gleb Natapov wrote: > > > Big real mode is fully emulated by KVM now, so if control is passed to > > the loaded kernel while one of the segment registers is in big real > > mode all the real mode part of the Linux start up is emulated. This > > slows boot process down. Fix that by resetting ES limit to 0xffff before > > jumping into the kernel. > > > > The patch also removes unused code segment definition from GDT and changes > > ES register to be 16bit in protected mode since CS stays 16bit too and > > it is CS segment that determines effective operands and addresses length. > > > > Signed-off-by: Gleb Natapov <gleb@redhat.com> > > I assume you tested that things still work, so the changes look ok to me. > Loaded kernel with kvm and tcg using -kernel/-initrd. > However, this patch should also include a binary patch to pc-bios/linuxboot.bin, since linuxboot.S doesn't get compiled into the .bin form on every machine. > > > Alex OK, something like this?: diff --git a/pc-bios/linuxboot.bin b/pc-bios/linuxboot.bin index e7c36694f997c3c34f7f4af3c2923bd2ef6094e7..435cac4ebff3fcd83cab4bf74de11f7071ab5aa6 100644 GIT binary patch delta 72 zcmZqRXyBNj#oWTwIZ^izW6s78X^grY3=9l?2hw%`DF%L}13f4D4!pei7sLaB|Nnu+ PBpBVlxtghlk#QmbUy&EH delta 68 zcmZqRXyBNj#azSGI8pZyW6H)4X^g52K)|nbpyx#2ftL^ef_NbC|38qJbsj=bI={J@ NsfKa#1||;1e*hia7ytkO > > > diff --git a/pc-bios/optionrom/linuxboot.S b/pc-bios/optionrom/linuxboot.S > > index 748c831..afe39a5 100644 > > --- a/pc-bios/optionrom/linuxboot.S > > +++ b/pc-bios/optionrom/linuxboot.S > > @@ -101,18 +101,20 @@ copy_kernel: > > mov $1, %eax > > mov %eax, %cr0 > > > > - /* So we can set ES to a 32-bit segment */ > > + /* So we can enlarge ES segment limit */ > > mov $0x10, %eax > > mov %eax, %es > > > > - /* We're now running in 16-bit CS, but 32-bit ES! */ > > - > > /* Load kernel and initrd */ > > read_fw_blob_addr32(FW_CFG_KERNEL) > > read_fw_blob_addr32(FW_CFG_INITRD) > > read_fw_blob_addr32(FW_CFG_CMDLINE) > > read_fw_blob_addr32(FW_CFG_SETUP) > > > > + /* Do not leave ES in big real mode */ > > + mov $0x08, %eax > > + mov %eax, %es > > + > > /* And now jump into Linux! */ > > mov $0, %eax > > mov %eax, %cr0 > > @@ -130,10 +132,10 @@ gdt: > > /* 0x00 */ > > .byte 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 > > > > - /* 0x08: code segment (base=0, limit=0xfffff, type=32bit code exec/read, DPL=0, 4k) */ > > -.byte 0xff, 0xff, 0x00, 0x00, 0x00, 0x9a, 0xcf, 0x00 > > + /* 0x08: data segment (base=0, limit=0xffff, type=16bit data read/write, DPL=0, 4k) */ > > +.byte 0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0x00, 0x00 > > > > - /* 0x10: data segment (base=0, limit=0xfffff, type=32bit data read/write, DPL=0, 4k) */ > > -.byte 0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0xcf, 0x00 > > + /* 0x10: data segment (base=0, limit=0xfffff, type=16bit data read/write, DPL=0, 4k) */ > > +.byte 0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0x8f, 0x00 > > > > BOOT_ROM_END > > -- > > Gleb. -- Gleb.
On 06.01.2013, at 13:56, Gleb Natapov wrote: > On Sun, Jan 06, 2013 at 01:47:17PM +0100, Alexander Graf wrote: >> >> On 06.01.2013, at 13:36, Gleb Natapov wrote: >> >>> Big real mode is fully emulated by KVM now, so if control is passed to >>> the loaded kernel while one of the segment registers is in big real >>> mode all the real mode part of the Linux start up is emulated. This >>> slows boot process down. Fix that by resetting ES limit to 0xffff before >>> jumping into the kernel. >>> >>> The patch also removes unused code segment definition from GDT and changes >>> ES register to be 16bit in protected mode since CS stays 16bit too and >>> it is CS segment that determines effective operands and addresses length. >>> >>> Signed-off-by: Gleb Natapov <gleb@redhat.com> >> >> I assume you tested that things still work, so the changes look ok to me. >> > Loaded kernel with kvm and tcg using -kernel/-initrd. Good. No objections from my side then. >> However, this patch should also include a binary patch to pc-bios/linuxboot.bin, since linuxboot.S doesn't get compiled into the .bin form on every machine. >> >> >> Alex > OK, something like this?: Looks like a binary patch, yes :). Alex
diff --git a/pc-bios/optionrom/linuxboot.S b/pc-bios/optionrom/linuxboot.S index 748c831..afe39a5 100644 --- a/pc-bios/optionrom/linuxboot.S +++ b/pc-bios/optionrom/linuxboot.S @@ -101,18 +101,20 @@ copy_kernel: mov $1, %eax mov %eax, %cr0 - /* So we can set ES to a 32-bit segment */ + /* So we can enlarge ES segment limit */ mov $0x10, %eax mov %eax, %es - /* We're now running in 16-bit CS, but 32-bit ES! */ - /* Load kernel and initrd */ read_fw_blob_addr32(FW_CFG_KERNEL) read_fw_blob_addr32(FW_CFG_INITRD) read_fw_blob_addr32(FW_CFG_CMDLINE) read_fw_blob_addr32(FW_CFG_SETUP) + /* Do not leave ES in big real mode */ + mov $0x08, %eax + mov %eax, %es + /* And now jump into Linux! */ mov $0, %eax mov %eax, %cr0 @@ -130,10 +132,10 @@ gdt: /* 0x00 */ .byte 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 - /* 0x08: code segment (base=0, limit=0xfffff, type=32bit code exec/read, DPL=0, 4k) */ -.byte 0xff, 0xff, 0x00, 0x00, 0x00, 0x9a, 0xcf, 0x00 + /* 0x08: data segment (base=0, limit=0xffff, type=16bit data read/write, DPL=0, 4k) */ +.byte 0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0x00, 0x00 - /* 0x10: data segment (base=0, limit=0xfffff, type=32bit data read/write, DPL=0, 4k) */ -.byte 0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0xcf, 0x00 + /* 0x10: data segment (base=0, limit=0xfffff, type=16bit data read/write, DPL=0, 4k) */ +.byte 0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0x8f, 0x00 BOOT_ROM_END
Big real mode is fully emulated by KVM now, so if control is passed to the loaded kernel while one of the segment registers is in big real mode all the real mode part of the Linux start up is emulated. This slows boot process down. Fix that by resetting ES limit to 0xffff before jumping into the kernel. The patch also removes unused code segment definition from GDT and changes ES register to be 16bit in protected mode since CS stays 16bit too and it is CS segment that determines effective operands and addresses length. Signed-off-by: Gleb Natapov <gleb@redhat.com> -- Gleb.