Re: [PATCH v5 06/11] x86/hvm: processor trace interface in HVM

[Michał Leszczyński <michal.leszczynski@xxxxxxx>]

----- 5 lip 2020 o 20:54, Michał Leszczyński michal.leszczynski@xxxxxxx 
napisał(a):

> From: Michal Leszczynski <michal.leszczynski@xxxxxxx>
> 
> Implement necessary changes in common code/HVM to support
> processor trace features. Define vmtrace_pt_* API and
> implement trace buffer allocation/deallocation in common
> code.
> 
> Signed-off-by: Michal Leszczynski <michal.leszczynski@xxxxxxx>
> ---
> xen/arch/x86/domain.c         | 19 +++++++++++++++++++
> xen/common/domain.c           | 19 +++++++++++++++++++
> xen/include/asm-x86/hvm/hvm.h | 20 ++++++++++++++++++++
> xen/include/xen/sched.h       |  4 ++++
> 4 files changed, 62 insertions(+)
> 
> diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
> index fee6c3931a..79c9794408 100644
> --- a/xen/arch/x86/domain.c
> +++ b/xen/arch/x86/domain.c
> @@ -2199,6 +2199,25 @@ int domain_relinquish_resources(struct domain *d)
>                 altp2m_vcpu_disable_ve(v);
>         }
> 
> +        for_each_vcpu ( d, v )
> +        {
> +            unsigned int i;
> +
> +            if ( !v->vmtrace.pt_buf )
> +                continue;
> +
> +            for ( i = 0; i < (v->domain->vmtrace_pt_size >> PAGE_SHIFT); i++ 
> )
> +            {
> +                struct page_info *pg = mfn_to_page(
> +                    mfn_add(page_to_mfn(v->vmtrace.pt_buf), i));
> +                if ( (pg->count_info & PGC_count_mask) != 1 )
> +                    return -EBUSY;
> +            }
> +
> +            free_domheap_pages(v->vmtrace.pt_buf,
> +                get_order_from_bytes(v->domain->vmtrace_pt_size));


While this works, I don't feel that this is a good solution with this loop
returning -EBUSY here. I would like to kindly ask for suggestions regarding
this topic.


Best regards,
Michał Leszczyński
CERT Polska