Re: [MINI-OS PATCH 12/19] mini-os: kexec: add support for handing over some memory across kexec

[Juergen Gross <jgross@xxxxxxxx>]

On 02.07.25 10:12, Juergen Gross wrote:
> Especially for support of Xenstore-stubdom live update some memory must
> be handed over to the new kernel without moving it around: as the
> 9pfs device used for storing and retrieving the state of Xenstore
> needs to be kept operational across kexec (it can't be reopened due to
> Xenstore not being available without access to the device), the ring
> pages need to be accessible via active grants by the backend all the
> time.
>
> Add the basic support for that by reserving a pre-defined number of
> memory pages at the top of the memory. This memory area will be
> handed over to the new kernel via specifying it as a module in
> struct hvm_start_info.
>
> The contents of the memory area are described via a generic table of
> contents in the last page of the memory.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>   Config.mk             |  2 ++
>   arch/x86/kexec.c      | 77 +++++++++++++++++++++++++++++++++++++++++++
>   arch/x86/mm.c         | 18 ++++++++++
>   arch/x86/setup.c      | 28 ++++++++++++++++
>   include/kernel.h      |  1 +
>   include/kexec.h       | 45 +++++++++++++++++++++++++
>   include/x86/arch_mm.h |  1 +
>   kexec.c               |  3 ++
>   mm.c                  |  6 ++++
>   9 files changed, 181 insertions(+)
>
> diff --git a/Config.mk b/Config.mk
> index b9675e61..0e4e86d8 100644
> --- a/Config.mk
> +++ b/Config.mk
> @@ -220,6 +220,8 @@ CONFIG-$(lwip) += CONFIG_LWIP
>   $(foreach i,$(CONFIG-y),$(eval $(i) ?= y))
>   $(foreach i,$(CONFIG-n),$(eval $(i) ?= n))
>   
> +CONFIG-val-$(CONFIG_KEXEC) += CONFIG_KEXEC_MODULE_PAGES
> +
>   $(foreach i,$(CONFIG-val-y),$(eval $(i) ?= 0))
>   
>   CONFIG-x += CONFIG_LIBXS
> diff --git a/arch/x86/kexec.c b/arch/x86/kexec.c
> index 804e7b6d..7fb98473 100644
> --- a/arch/x86/kexec.c
> +++ b/arch/x86/kexec.c
> @@ -201,10 +201,73 @@ static unsigned long kexec_param_loc;
>   static unsigned int kexec_param_size;
>   static unsigned long kexec_param_mem;
>   
> +static struct kexec_module *kexec_check_module(void)
> +{
> +    unsigned long mod_size;
> +    unsigned long mod;
> +    struct kexec_module *module_ptr;
> +
> +    mod = get_module(&mod_size);
> +    if ( !mod )
> +        return NULL;
> +    /* Size must be a multiple of PAGE_SIZE. */
> +    if ( mod_size & ~PAGE_MASK )
> +        return NULL;
> +
> +    /* Kxec module description is at start of the last page of the module. */
> +    module_ptr = (void *)(mod + mod_size - (unsigned long)PAGE_SIZE);
> +
> +    /* Check eye catcher. */
> +    if ( memcmp(module_ptr->eye_catcher, KEXECMOD_EYECATCHER,
> +                sizeof(module_ptr->eye_catcher)) )
> +        return NULL;
> +    if ( module_ptr->n_pages != (mod_size >> PAGE_SHIFT) - 1 )
> +        return NULL;
There is missing:

+    kexec_mod_start = mod;

Otherwise a second live update won't work.

I'll wait for more feedback before sending out V2.


Juergen

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