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Re: [PATCH v3 3/4] xen/arm: vgic: free eSPIs using the bitmap index
- To: "Orzel, Michal" <michal.orzel@xxxxxxx>
- From: Mykola Kvach <mykola_kvach@xxxxxxxx>
- Date: Tue, 22 Sep 2026 08:26:12 +0300
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- Cc: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>
- Delivery-date: Tue, 22 Sep 2026 05:26:25 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Mail-followup-to: "Orzel, Michal" <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>
On Mon, Sep 14, 2026 at 05:55:29PM +0200, Orzel, Michal wrote:
>
>
> On 25-Aug-26 02:35, Volodymyr Babchuk wrote:
> > Hi,
> >
> >
> > I have only one small question to this patch. Please see below.
> >
> > Mykola Kvach <mykola_kvach@xxxxxxxx> writes:
> >
> >> The allocated_irqs bitmap in the existing vGIC implementation stores eSPI
> >> allocation bits immediately after the regular vIRQ bits.
> >> vgic_reserve_virq() converts an eSPI INTID to this compressed bitmap index,
> >> but vgic_free_virq() used the raw INTID.
> >>
> >> Freeing INTID 4096 therefore clears bit 4096 instead of the first eSPI bit.
> >> This writes beyond allocated_irqs and leaves the intended eSPI bit set.
> >> Valid eSPIs reach this path during DOMCTL bind failure cleanup and unbind,
> >> and during vPL011 teardown.
> >>
> >> Add virq_to_idx(), the inverse of idx_to_virq(), and use it when reserving
> >> and freeing vIRQs. Validate a vIRQ before clearing its allocation bit.
> >>
> >> Fixes: bdde400c6e1b ("xen/arm: vgic: add resource management for extended
> >> SPIs")
> >> Signed-off-by: Mykola Kvach <mykola_kvach@xxxxxxxx>
> >> ---
> >> Changes in v3:
> >> - Adapt virq_to_idx() to the configuration-neutral is_espi() helper.
> >>
> >> Changes in v2:
> >> - Call is_espi() without a configuration guard.
> >> ---
> >> xen/arch/arm/vgic.c | 27 ++++++++++++++++-----------
> >> 1 file changed, 16 insertions(+), 11 deletions(-)
> >>
> >> diff --git a/xen/arch/arm/vgic.c b/xen/arch/arm/vgic.c
> >> index e14123a30a..e541348a5c 100644
> >> --- a/xen/arch/arm/vgic.c
> >> +++ b/xen/arch/arm/vgic.c
> >> @@ -33,6 +33,16 @@ static inline unsigned int idx_to_virq(struct domain
> >> *d, unsigned int idx)
> >> return idx;
> >> }
> >>
> >> +static inline unsigned int virq_to_idx(struct domain *d, unsigned int
> >> virq)
> Please add a comment at the top of the function about the layout these two
> helpers encode to prevent such problems in the future.
Ack.
Best regards,
Mykola
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