Re: [SeaBIOS] [PATCH v3 2/2] Boot Linux using QEMU fw_cfg DMA interface

[Marc Marí]

On Fri, 18 Sep 2015 14:40:30 -0400
"Kevin O'Connor"  wrote:
> On Fri, Sep 18, 2015 at 10:59:15AM +0200, Marc Marí wrote:
> > Reading Linux from the fw_cfg interface is faster using the DMA
> > interface. For this reason, add a Linux loader that can benefit
> > from this interface.
> > Signed-off-by: Marc Marí
> >
> > src/boot.c        | 32 ++++++++++++++++-----
> >  src/fw/paravirt.c | 85
> > ++++++++++++++++++++++++++++++++++++++++++++-----------
> > src/fw/paravirt.h | 36 +++++++++++++++++++++++ src/post.c        |
> > 1 + src/romlayout.S   | 20 +++++++++++++
> >  src/util.h        |  1 +
> >  6 files changed, 152 insertions(+), 23 deletions(-)
> >
> > diff --git a/src/boot.c b/src/boot.c
> > index e0f73a3..52918f8 100644
> > --- a/src/boot.c
> > +++ b/src/boot.c
> > @@ -300,13 +300,14 @@ struct bootentry_s {
> >  };
> >  static struct hlist_head BootList VARVERIFY32INIT;
> >
> > -#define IPL_TYPE_FLOPPY      0x01
> > -#define IPL_TYPE_HARDDISK    0x02
> > -#define IPL_TYPE_CDROM       0x03
> > -#define IPL_TYPE_CBFS        0x20
> > -#define IPL_TYPE_BEV         0x80
> > -#define IPL_TYPE_BCV         0x81
> > -#define IPL_TYPE_HALT        0xf0
> > +#define IPL_TYPE_FLOPPY         0x01
> > +#define IPL_TYPE_HARDDISK       0x02
> > +#define IPL_TYPE_CDROM          0x03
> > +#define IPL_TYPE_CBFS           0x20
> > +#define IPL_TYPE_QEMU_VMLINUX   0x21
> > +#define IPL_TYPE_BEV            0x80
> > +#define IPL_TYPE_BCV            0x81
> > +#define IPL_TYPE_HALT           0xf0
> >
> > static void
> >  bootentry_add(int type, int prio, u32 data, const char *desc)
> > @@ -398,6 +399,12 @@ boot_add_cbfs(void *data, const char *desc,
> > int prio) bootentry_add(IPL_TYPE_CBFS, defPrio(prio, DEFAULT_PRIO),
> > (u32)data, desc); }
> >
> > +// Add a FW_CFG DMA boot
> > +void
> > +boot_add_qemu_vmlinux(const char *desc, int prio)
> > +{
> > bootentry_add(IPL_TYPE_QEMU_VMLINUX, defPrio(prio,
> >
> > DEFAULT_PRIO), 0, desc); +}
> >
> > /****************************************************************
> > Keyboard calls
> >
> > @@ -684,6 +691,14 @@ boot_rom(u32 vector)
> >      call_boot_entry(so, 0);
> >  }
> >
> > +// Boot from a linuxboot ROM when QEMU cfg is in DMA mode
> > +static void
> > +boot_qemu_vmlinux_dma(void)
> > +{
> > printf("Booting Linux from fw_cfg...\n");
> > qemu_vmlinux_dma_boot();
> >
> > +}
> >
> > // Unable to find bootable device - warn user and eventually retry.
> >  static void
> >  boot_fail(void)
> > @@ -734,6 +749,9 @@ do_boot(int seq_nr)
> >      case IPL_TYPE_BEV:
> >          boot_rom(ie->vector);
> >          break;
> > case IPL_TYPE_QEMU_VMLINUX:
> >    boot_qemu_vmlinux_dma();
> >    break;
> > case IPL_TYPE_HALT:
> >        boot_fail();
> >        break;
> >
> > diff --git a/src/fw/paravirt.c b/src/fw/paravirt.c
> > index 65f9fba..6896511 100644
> > --- a/src/fw/paravirt.c
> > +++ b/src/fw/paravirt.c
> > @@ -23,7 +23,8 @@
> >  #include "util.h" // pci_setup
> >  #include "x86.h" // cpuid
> >  #include "xen.h" // xen_biostable_setup
> > -#include "stacks.h" // yield
> > +#include "bregs.h" // struct bregs
> > +#include "stacks.h" // farcall16big, yield
> >
> > // Amount of continuous ram under 4Gig
> >  u32 RamSize;
> > @@ -185,21 +186,6 @@ qemu_platform_setup(void)
> > QEMU firmware config (fw_cfg) interface
> >
> > ****************************************************************/
> >
> > -// List of QEMU fw_cfg entries.  DO NOT ADD MORE.  (All new content
> > -// should be passed via the fw_cfg "file" interface.)
> > -#define QEMU_CFG_SIGNATURE              0x00
> > -#define QEMU_CFG_ID                     0x01
> > -#define QEMU_CFG_UUID                   0x02
> > -#define QEMU_CFG_NUMA                   0x0d
> > -#define QEMU_CFG_BOOT_MENU              0x0e
> > -#define QEMU_CFG_MAX_CPUS               0x0f
> > -#define QEMU_CFG_FILE_DIR               0x19
> > -#define QEMU_CFG_ARCH_LOCAL             0x8000
> > -#define QEMU_CFG_ACPI_TABLES            (QEMU_CFG_ARCH_LOCAL + 0)
> > -#define QEMU_CFG_SMBIOS_ENTRIES         (QEMU_CFG_ARCH_LOCAL + 1)
> > -#define QEMU_CFG_IRQ0_OVERRIDE          (QEMU_CFG_ARCH_LOCAL + 2)
> > -#define QEMU_CFG_E820_TABLE             (QEMU_CFG_ARCH_LOCAL + 3)
> >
> > static void
> >  qemu_cfg_select(u16 f)
> >  {
> > @@ -509,3 +495,70 @@ void qemu_cfg_init(void)
> >          dprintf(1, "Moving pm_base to 0x%x\n", acpi_pm_base);
> >      }
> >  }
> >
> > +void qemu_vmlinux_dma_boot(void)
> > +{
> > dprintf(1, "Loading kernel\n");
> > irq_disable();
>
> SeaBIOS always disabled interrupts in C code (see
> http://www.seabios.org/Execution_and_code_flow#Hardware_interrupts ),
> so this irq_disable() is not needed.
> > void *setup_addr;
> > u32 setup_size;
> > qemu_cfg_read_entry(&setup_addr, QEMU_CFG_SETUP_ADDR, 4);
> > qemu_cfg_read_entry(&setup_size, QEMU_CFG_SETUP_SIZE, 4);
> > qemu_cfg_read_entry(setup_addr, QEMU_CFG_SETUP_DATA,
> >
> > setup_size); +
> > u16 protocol = readw(setup_addr + 0x206);
> > if (protocol < 0x203) {
> >    /* Assume initrd_max 0x37ffffff */
> >    writel(setup_addr + 0x22c, 0x37ffffff);
> > }
> > void *initrd_addr;
> > u32 initrd_size;
> > qemu_cfg_read_entry(&initrd_addr, QEMU_CFG_INITRD_ADDR, 4);
> > qemu_cfg_read_entry(&initrd_size, QEMU_CFG_INITRD_SIZE, 4);
> > u32 initrd_end_page = (u32)(initrd_addr + initrd_size) & -4096;
> > u32 max_allowed_page = readl(setup_addr + 0x22c) & -4096;
>
> Use of the ALIGN_DOWN() macro would be preferable here.
> > if (initrd_end_page != max_allowed_page) {
> >    /* Initrd at the end of memory. Compute better initrd
> >
> > address
> >     * based on e801 data
> >     */
> >    initrd_addr = (void *)((LegacyRamSize - initrd_size) &
> >
> > -4096);
> >    writel(setup_addr + 0x218, (u32)initrd_addr);
> > }
> > qemu_cfg_read_entry(initrd_addr, QEMU_CFG_INITRD_DATA,
> >
> > initrd_size); +
> > void *kernel_addr;
> > u32 kernel_size;
> > qemu_cfg_read_entry(&kernel_addr, QEMU_CFG_KERNEL_ADDR, 4);
> > qemu_cfg_read_entry(&kernel_size, QEMU_CFG_KERNEL_SIZE, 4);
> > qemu_cfg_read_entry(kernel_addr, QEMU_CFG_KERNEL_DATA,
> >
> > kernel_size); +
> > void *cmdline_addr;
> > u32 cmdline_size;
> > qemu_cfg_read_entry(&cmdline_addr, QEMU_CFG_CMDLINE_ADDR, 4);
> > qemu_cfg_read_entry(&cmdline_size, QEMU_CFG_CMDLINE_SIZE, 4);
> > qemu_cfg_read_entry(cmdline_addr, QEMU_CFG_CMDLINE_DATA,
> >
> > cmdline_size); +
> > dprintf(1, "Jumping to kernel %d@%x %d@%x %d@%x %d@%x\n"
> >        , setup_size, (u32)setup_addr, cmdline_size,
> >
> > (u32)cmdline_addr
> >        , kernel_size, (u32)kernel_addr, initrd_size,
> >
> > (u32)initrd_addr);
> > struct bregs br;
> > memset(&br, 0, sizeof(br));
> > extern void kernel_stub(void);
> > br.ebx = (u32)setup_addr >> 4;
> > br.edx = (u32)cmdline_addr - (u32)setup_addr - 16;
> > br.code = SEGOFF(SEG_BIOS, (u32)kernel_stub - BUILD_BIOS_ADDR);
> > farcall16big(&br);
> >
> > +}
> >
> > +void qemu_vmlinux_dma_setup(void) {
> > if (qemu_cfg_dma_enabled()) {
>
> I don't think this feature should depend on DMA (it works fine even if
> fw_cfg DMA is not available).  I also don't think "dma" should be in
> the function names - qemu_vmlinux_setup() is fine.
>
> Also, the code should check if there is a kernel before registering an
> IPL - for example:
> u32 kernel_size;
> qemu_cfg_read_entry(&kernel_size, QEMU_CFG_KERNEL_SIZE,
>
> sizeof(kernel_size)); if (!kernel_size)
>         return;
> >    boot_add_qemu_vmlinux("QEMU Kernel image",
> >
> > bootprio_find_named_rom("genroms/linuxboot.bin", 0));
>
> Using "genroms/linuxboot.bin" works for testing, but I think a new
> bootorder id (eg, "vmlinux") will need to be defined between QEMU and
> SeaBIOS.  I don't think it would be good to overload the meaning of
> the "genroms/" prefix.

I was looking at it, but I don't see a "good" way to put it.

If you want to boot from fw_cfg through linuxboot.S, you prefer to boot
using fw_cfg DMA, which is faster. And adding a new entry would mean
adding a new type (?) which would be added in the same cases as
linuxboot.S. It looks a lot of work for a thing that is repeated.

But yes, it's really ugly to overload it in this way.

Any other ideas?

Marc
> Otherwise the series looks good to me.  Once the QEMU series is
> committed we can commit this series to SeaBIOS.
>
> -Kevin