Re: [Xen-devel] [PATCH v8 3/5] xen/mem_sharing: VM forking

[Andrew Cooper]

On 10/02/2020 19:21, Tamas K Lengyel wrote:
> diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
> index 3835bc928f..ccf338918d 100644
> --- a/xen/arch/x86/mm/mem_sharing.c
> +++ b/xen/arch/x86/mm/mem_sharing.c
> @@ -36,6 +37,9 @@
>  #include <asm/altp2m.h>
>  #include <asm/atomic.h>
>  #include <asm/event.h>
> +#include <asm/hap.h>
> +#include <asm/hvm/hvm.h>
> +#include <asm/hvm/save.h>

This include is stale, I think.

> +static void fork_tsc(struct domain *cd, struct domain *d)
> +{
> +    uint32_t tsc_mode;
> +    uint32_t gtsc_khz;
> +    uint32_t incarnation;
> +    uint64_t elapsed_nsec;
> +
> +    tsc_get_info(d, &tsc_mode, &elapsed_nsec, &gtsc_khz, &incarnation);
> +    tsc_set_info(cd, tsc_mode, elapsed_nsec, gtsc_khz, incarnation);

Sadly, get and set are asymetric.  For reasons best understood by the
original authors, incarnation gets automatically incremented on set,
rather than happing as part of migration where it logically lives.

As a result, you probably want to set incarnation - 1, and leave a
comment saying "Don't bump the incarnation" or similar.

~Andrew

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