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Re: [XEN][PATCH 0/5] x86: pvh: allow to disable 32-bit (COMPAT) interface support
- To: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 12 Nov 2025 07:50:04 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>, Jason Andryuk <jason.andryuk@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 12 Nov 2025 06:50:15 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 11.11.2025 18:54, Grygorii Strashko wrote:
> This series introduces possibility to disable 32-bit (COMPAT) interface
> support
> in the following cases:
The use of plural here ...
> - Only PVH domains are used
> - Guests (OS) are started by using direct Direct Kernel Boot
> - Guests (OS) are 64-bit and Guest early boot code, which is running not
> in 64-bit mode, does not access Xen interfaces
> (hypercalls, shared_info, ..)
... makes this an OR list, which I don't think would be correct. PVH domains,
for example, can well be 32-bit ones, can't they? Otoh the latter two points
look as if they really enumerate alternatives. Can you clarify please what is
meant?
Jan
> If above criterias are met the COMPAT HVM interface become unreachable and
> can be disabled.
> Coverage reports analyze and adding guard (debug) exceptions in
> hvm_hypercall/hvm_do_multicall_call
> and hvm_latch_shinfo_size() confirm that COMPAT HVM interface is unused for
> safety use-case.
>
> Grygorii Strashko (5):
> x86: hvm: dm: factor out compat code under ifdefs
> x86: hvm: compat: introduce vcpu_is_hcall_compat() helper
> x86: hvm: factor out compat code under ifdefs
> x86: pvh: allow to disable 32-bit interface support
> x86: constify has_32bit_shinfo() if !CONFIG_COMPAT
>
> xen/arch/x86/hvm/Kconfig | 19 +++++++++++++++-
> xen/arch/x86/hvm/dm.c | 2 ++
> xen/arch/x86/hvm/hvm.c | 22 +++++++++++++-----
> xen/arch/x86/hvm/hypercall.c | 37 +++++++++++++++++++++++--------
> xen/arch/x86/hypercall.c | 6 +----
> xen/arch/x86/include/asm/domain.h | 3 ++-
> xen/common/kernel.c | 2 +-
> xen/include/xen/sched.h | 9 ++++++++
> 8 files changed, 78 insertions(+), 22 deletions(-)
>
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