Re: [Xen-devel] [PATCH] xen/arm: flush icache as well when XEN_DOMCTL_cacheflush is issued

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Jan 26, 2017 at 03:16:22PM -0700, Tamas K Lengyel wrote:
> When the toolstack modifies memory of a running ARM VM it may happen
> that the underlying memory of a current vCPU PC is changed. Without
> flushing the icache the vCPU may continue executing stale instructions.
> 

Why is this not an issue for x86? Is this because ARM handles coherency
differently from x86?

> In this patch we introduce VA-based icache flushing macros. Also expose
> the xc_domain_cacheflush through xenctrl.h.
> 
> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
> ---
> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx>
> 
> Note: patch has been verified to solve stale icache issues on the
>       HiKey platform.
> ---
>  tools/libxc/include/xenctrl.h    |  6 ++++++
>  tools/libxc/xc_private.h         |  3 ---
>  xen/arch/arm/mm.c                |  1 +
>  xen/include/asm-arm/arm32/page.h |  3 +++
>  xen/include/asm-arm/arm64/page.h |  3 +++
>  xen/include/asm-arm/page.h       | 31 +++++++++++++++++++++++++++++++
>  6 files changed, 44 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/libxc/include/xenctrl.h b/tools/libxc/include/xenctrl.h
> index 63c616ff6a..cb80a2b07c 100644
> --- a/tools/libxc/include/xenctrl.h
> +++ b/tools/libxc/include/xenctrl.h
> @@ -2720,6 +2720,12 @@ int xc_livepatch_revert(xc_interface *xch, char *name, 
> uint32_t timeout);
>  int xc_livepatch_unload(xc_interface *xch, char *name, uint32_t timeout);
>  int xc_livepatch_replace(xc_interface *xch, char *name, uint32_t timeout);
>  
> +/*
> + * ARM only. Ensure cache coherency after memory modifications.
> + */

The existing code doesn't suggest this is ARM only. This function is
used in xc_dom_unmap_one etc. This comment looks wrong.

I don't object to making this function externally visible though.

Wei.

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