Since linux commit: cf8fa920cb42 ("i386: handle an initrd in highmem (version 2)")
linux has supported initrd up to 4 GB, but the header field
ramdisk_max is still set to 2 GB to avoid "possible bootloader bugs".
When use '-kernel vmlinux -initrd initrd.cgz' to launch a VM,
the firmware(it could be linuxboot_dma.bin) helps to read initrd
contents into guest memory(below ramdisk_max) and jump to kernel.
that's similar with what bootloader does, like grub.
In addition, initrd_max is uint32_t simply because QEMU doesn't support
the 64-bit boot protocol (specifically the ext_ramdisk_image field).
Therefore here just limit initrd_max to UINT32_MAX simply as well to
allow initrd to be loaded below 4 GB.
CC: Paolo Bonzini <pbonzini@redhat.com>
CC: Richard Henderson <rth@twiddle.net>
CC: Eduardo Habkost <ehabkost@redhat.com>
CC: "Michael S. Tsirkin" <mst@redhat.com>
CC: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
---
V5: udpate comments and changelog
V3: correct grammar and check XLF_CAN_BE_LOADED_ABOVE_4G first (Michael S. Tsirkin)
Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
---
hw/i386/pc.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 89c25b2..ea7a3c7 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -904,7 +904,29 @@ static void load_linux(PCMachineState *pcms,
#endif
/* highest address for loading the initrd */
- if (protocol >= 0x203) {
+ if (protocol >= 0x20c &&
+ lduw_p(header+0x236) & XLF_CAN_BE_LOADED_ABOVE_4G) {
+ /*
+ * Linux has supported initrd up to 4 GB for a very long time (2007,
+ * long before XLF_CAN_BE_LOADED_ABOVE_4G which was added in 2013),
+ * though it only sets initrd_max to 2 GB to "work around bootloader
+ * bugs". Luckily, QEMU firmware(which does something like bootloader)
+ * has supported this.
+ *
+ * It's believed that if XLF_CAN_BE_LOADED_ABOVE_4G is set, initrd can
+ * be loaded into any address.
+ *
+ * In addition, initrd_max is uint32_t simply because QEMU doesn't
+ * support the 64-bit boot protocol (specifically the ext_ramdisk_image
+ * field).
+ *
+ * Therefore here just limit initrd_max to UINT32_MAX simply as well.
+ *
+ * FIXME: it's possible that linux protocol within [0x208, 0x20c]
+ * supports up to 4G initrd as well.
+ */
+ initrd_max = UINT32_MAX;
+ } else if (protocol >= 0x203) {
initrd_max = ldl_p(header+0x22c);
} else {
initrd_max = 0x37ffffff;
--
2.7.4
On Fri, Jan 11, 2019 at 04:57:51PM +0800, Li Zhijian wrote:
> Since linux commit: cf8fa920cb42 ("i386: handle an initrd in highmem (version 2)")
> linux has supported initrd up to 4 GB, but the header field
> ramdisk_max is still set to 2 GB to avoid "possible bootloader bugs".
>
> When use '-kernel vmlinux -initrd initrd.cgz' to launch a VM,
> the firmware(it could be linuxboot_dma.bin) helps to read initrd
> contents into guest memory(below ramdisk_max) and jump to kernel.
> that's similar with what bootloader does, like grub.
>
> In addition, initrd_max is uint32_t simply because QEMU doesn't support
> the 64-bit boot protocol (specifically the ext_ramdisk_image field).
>
> Therefore here just limit initrd_max to UINT32_MAX simply as well to
> allow initrd to be loaded below 4 GB.
>
> CC: Paolo Bonzini <pbonzini@redhat.com>
> CC: Richard Henderson <rth@twiddle.net>
> CC: Eduardo Habkost <ehabkost@redhat.com>
> CC: "Michael S. Tsirkin" <mst@redhat.com>
> CC: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
> Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
>
> ---
> V5: udpate comments and changelog
> V3: correct grammar and check XLF_CAN_BE_LOADED_ABOVE_4G first (Michael S. Tsirkin)
>
> Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> ---
> hw/i386/pc.c | 24 +++++++++++++++++++++++-
> 1 file changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 89c25b2..ea7a3c7 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -904,7 +904,29 @@ static void load_linux(PCMachineState *pcms,
> #endif
>
> /* highest address for loading the initrd */
> - if (protocol >= 0x203) {
> + if (protocol >= 0x20c &&
> + lduw_p(header+0x236) & XLF_CAN_BE_LOADED_ABOVE_4G) {
> + /*
> + * Linux has supported initrd up to 4 GB for a very long time (2007,
> + * long before XLF_CAN_BE_LOADED_ABOVE_4G which was added in 2013),
> + * though it only sets initrd_max to 2 GB to "work around bootloader
> + * bugs". Luckily, QEMU firmware(which does something like bootloader)
> + * has supported this.
> + *
> + * It's believed that if XLF_CAN_BE_LOADED_ABOVE_4G is set, initrd can
> + * be loaded into any address.
> + *
> + * In addition, initrd_max is uint32_t simply because QEMU doesn't
> + * support the 64-bit boot protocol (specifically the ext_ramdisk_image
> + * field).
> + *
> + * Therefore here just limit initrd_max to UINT32_MAX simply as well.
> + *
> + * FIXME: it's possible that linux protocol within [0x208, 0x20c]
> + * supports up to 4G initrd as well.
I don't understand what exactly this FIXME comment is
documenting. What exactly needs to be fixed?
> + */
> + initrd_max = UINT32_MAX;
> + } else if (protocol >= 0x203) {
> initrd_max = ldl_p(header+0x22c);
> } else {
> initrd_max = 0x37ffffff;
> --
> 2.7.4
>
--
Eduardo
Hi Eduardo
On 1/15/19 01:53, Eduardo Habkost wrote:
>> + if (protocol >= 0x20c &&
>> + lduw_p(header+0x236) & XLF_CAN_BE_LOADED_ABOVE_4G) {
>> + /*
>> + * Linux has supported initrd up to 4 GB for a very long time (2007,
>> + * long before XLF_CAN_BE_LOADED_ABOVE_4G which was added in 2013),
>> + * though it only sets initrd_max to 2 GB to "work around bootloader
>> + * bugs". Luckily, QEMU firmware(which does something like bootloader)
>> + * has supported this.
>> + *
>> + * It's believed that if XLF_CAN_BE_LOADED_ABOVE_4G is set, initrd can
>> + * be loaded into any address.
>> + *
>> + * In addition, initrd_max is uint32_t simply because QEMU doesn't
>> + * support the 64-bit boot protocol (specifically the ext_ramdisk_image
>> + * field).
>> + *
>> + * Therefore here just limit initrd_max to UINT32_MAX simply as well.
>> + *
>> + * FIXME: it's possible that linux protocol within [0x208, 0x20c]
>> + * supports up to 4G initrd as well.
> I don't understand what exactly this FIXME comment is
> documenting. What exactly needs to be fixed?
>
XLF_CAN_BE_LOADED_ABOVE_4G is one of the indicators, actually as comments said,
linux has supported up to 4 GB initrd since linux-2.26(protocol version 0x208).
I just want to comment that linux with protocol within [0x208, 0x20c] supports up to 4 GB initrd as well.
Is documenting with FIXME appropriate?
Thanks
On Tue, Jan 15, 2019 at 09:35:09AM +0800, Li Zhijian wrote:
> Hi Eduardo
>
>
> On 1/15/19 01:53, Eduardo Habkost wrote:
>
> + if (protocol >= 0x20c &&
> + lduw_p(header+0x236) & XLF_CAN_BE_LOADED_ABOVE_4G) {
> + /*
> + * Linux has supported initrd up to 4 GB for a very long time (2007,
> + * long before XLF_CAN_BE_LOADED_ABOVE_4G which was added in 2013),
> + * though it only sets initrd_max to 2 GB to "work around bootloader
> + * bugs". Luckily, QEMU firmware(which does something like bootloader)
> + * has supported this.
> + *
> + * It's believed that if XLF_CAN_BE_LOADED_ABOVE_4G is set, initrd can
> + * be loaded into any address.
> + *
> + * In addition, initrd_max is uint32_t simply because QEMU doesn't
> + * support the 64-bit boot protocol (specifically the ext_ramdisk_image
> + * field).
> + *
> + * Therefore here just limit initrd_max to UINT32_MAX simply as well.
> + *
> + * FIXME: it's possible that linux protocol within [0x208, 0x20c]
> + * supports up to 4G initrd as well.
>
> I don't understand what exactly this FIXME comment is
> documenting. What exactly needs to be fixed?
>
>
> XLF_CAN_BE_LOADED_ABOVE_4G is one of the indicators, actually as comments said,
> linux has supported up to 4 GB initrd since linux-2.26(protocol version 0x208).
>
>
> I just want to comment that linux with protocol within [0x208, 0x20c] supports up to 4 GB initrd as well.
>
> Is documenting with FIXME appropriate?
>
>
> Thanks
>
>
Fixme should say what is missing in the qemu implementation.
E.g.
/*
* Bar 2010 and up can actually be supported using foo.
* FIXME: make use of foo to support bar.
*/
--
MST
Hi Michael, Eduardo
On 1/15/19 09:46, Michael S. Tsirkin wrote:
> On Tue, Jan 15, 2019 at 09:35:09AM +0800, Li Zhijian wrote:
>> Hi Eduardo
>>
>>
>> On 1/15/19 01:53, Eduardo Habkost wrote:
>>
>> + if (protocol >= 0x20c &&
>> + lduw_p(header+0x236) & XLF_CAN_BE_LOADED_ABOVE_4G) {
>> + /*
>> + * Linux has supported initrd up to 4 GB for a very long time (2007,
>> + * long before XLF_CAN_BE_LOADED_ABOVE_4G which was added in 2013),
>> + * though it only sets initrd_max to 2 GB to "work around bootloader
>> + * bugs". Luckily, QEMU firmware(which does something like bootloader)
>> + * has supported this.
>> + *
>> + * It's believed that if XLF_CAN_BE_LOADED_ABOVE_4G is set, initrd can
>> + * be loaded into any address.
>> + *
>> + * In addition, initrd_max is uint32_t simply because QEMU doesn't
>> + * support the 64-bit boot protocol (specifically the ext_ramdisk_image
>> + * field).
>> + *
>> + * Therefore here just limit initrd_max to UINT32_MAX simply as well.
>> + *
>> + * FIXME: it's possible that linux protocol within [0x208, 0x20c]
>> + * supports up to 4G initrd as well.
>>
>> I don't understand what exactly this FIXME comment is
>> documenting. What exactly needs to be fixed?
>>
>>
>> XLF_CAN_BE_LOADED_ABOVE_4G is one of the indicators, actually as comments said,
>> linux has supported up to 4 GB initrd since linux-2.26(protocol version 0x208).
>>
>>
>> I just want to comment that linux with protocol within [0x208, 0x20c] supports up to 4 GB initrd as well.
>>
>> Is documenting with FIXME appropriate?
>>
>>
>> Thanks
>>
>>
>
> Fixme should say what is missing in the qemu implementation.
thanks for your explanation @Michael
I'd like to update "FIXME" to "NOTE" and move it into git-commit-log if no objection
and it's okay to delete it simply if it confuses others :)
BTW: any other comments for the others
Thanks
Zhijian
> E.g.
>
> /*
> * Bar 2010 and up can actually be supported using foo.
> * FIXME: make use of foo to support bar.
> */
>
>
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