Re: [PATCH 4/4] ARM/vgic: Use for_each_set_bit() in vgic-mmio*

[Michal Orzel <michal.orzel@xxxxxxx>]

On 02/09/2024 12:03, Andrew Cooper wrote:
> 
> 
> These are all loops over a scalar value, and don't need to call general bitop
> helpers behind the scenes.
> 
> No functional change.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Julien Grall <julien@xxxxxxx>
> CC: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
> CC: Bertrand Marquis <bertrand.marquis@xxxxxxx>
> CC: Michal Orzel <michal.orzel@xxxxxxx>
> 
> Slighly RFC.  It's unclear whether len is the size of the register, or the
> size of the access.  For sub-GPR accesses, won't the upper bits be clear
> anyway?  If so, this can be simplified further.
See dispatch_mmio_write(). "len" refers to access size (i.e. 1/4/8 bytes). Each 
register is defined
with a region access i.e. VGIC_ACCESS_32bit that is compared with the actual 
access. In the current code
there is no register with 8B access. If there is a mismatch, there will be a 
data abort injected.
Also, the top 32-bits are not cleared anywhere, so I don't think we can drop 
masking. @Julien?

> 
> $ ../scripts/bloat-o-meter xen-syms-arm64-{before,after}
> add/remove: 0/0 grow/shrink: 2/5 up/down: 20/-140 (-120)
> Function                                     old     new   delta
> vgic_mmio_write_spending                     320     332     +12
> vgic_mmio_write_cpending                     368     376      +8
> vgic_mmio_write_sactive                      192     176     -16
> vgic_mmio_write_cactive                      192     176     -16
> vgic_mmio_write_cenable                      316     288     -28
> vgic_mmio_write_senable                      320     284     -36
> vgic_mmio_write_sgir                         344     300     -44
> 
> $ ../scripts/bloat-o-meter xen-syms-arm32-{before,after}
> add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-32 (-32)
> Function                                     old     new   delta
> vgic_mmio_write_sactive                      204     200      -4
> vgic_mmio_write_cpending                     464     460      -4
> vgic_mmio_write_cactive                      204     200      -4
> vgic_mmio_write_sgir                         336     316     -20
> ---
>  xen/arch/arm/vgic/vgic-mmio-v2.c |  3 +--
>  xen/arch/arm/vgic/vgic-mmio.c    | 36 +++++++++++++++++++++-----------
>  2 files changed, 25 insertions(+), 14 deletions(-)
> 
> diff --git a/xen/arch/arm/vgic/vgic-mmio-v2.c 
> b/xen/arch/arm/vgic/vgic-mmio-v2.c
> index 670b335db2c3..42fac0403f07 100644
> --- a/xen/arch/arm/vgic/vgic-mmio-v2.c
> +++ b/xen/arch/arm/vgic/vgic-mmio-v2.c
> @@ -90,7 +90,6 @@ static void vgic_mmio_write_sgir(struct vcpu *source_vcpu,
>      unsigned int intid = val & GICD_SGI_INTID_MASK;
>      unsigned long targets = (val & GICD_SGI_TARGET_MASK) >>
>                              GICD_SGI_TARGET_SHIFT;
> -    unsigned int vcpu_id;
> 
>      switch ( val & GICD_SGI_TARGET_LIST_MASK )
>      {
> @@ -108,7 +107,7 @@ static void vgic_mmio_write_sgir(struct vcpu *source_vcpu,
>          return;
>      }
> 
> -    bitmap_for_each ( vcpu_id, &targets, 8 )
> +    for_each_set_bit ( vcpu_id, (uint8_t)targets )
>      {
>          struct vcpu *vcpu = d->vcpu[vcpu_id];
>          struct vgic_irq *irq = vgic_get_irq(d, vcpu, intid);
> diff --git a/xen/arch/arm/vgic/vgic-mmio.c b/xen/arch/arm/vgic/vgic-mmio.c
> index bd4caf7fc326..f7c336a238ab 100644
> --- a/xen/arch/arm/vgic/vgic-mmio.c
> +++ b/xen/arch/arm/vgic/vgic-mmio.c
> @@ -69,9 +69,11 @@ void vgic_mmio_write_senable(struct vcpu *vcpu,
>                               unsigned long val)
>  {
>      uint32_t intid = VGIC_ADDR_TO_INTID(addr, 1);
> -    unsigned int i;
> 
> -    bitmap_for_each ( i, &val, len * 8 )
> +    if ( len < sizeof(val) )
> +        val &= (1UL << (len * 8)) - 1;
> +
> +    for_each_set_bit ( i, val )
>      {
>          struct vgic_irq *irq = vgic_get_irq(vcpu->domain, vcpu, intid + i);
>          unsigned long flags;
> @@ -114,9 +116,11 @@ void vgic_mmio_write_cenable(struct vcpu *vcpu,
>                               unsigned long val)
>  {
>      uint32_t intid = VGIC_ADDR_TO_INTID(addr, 1);
> -    unsigned int i;
> 
> -    bitmap_for_each ( i, &val, len * 8 )
> +    if ( len < sizeof(val) )
> +        val &= (1UL << (len * 8)) - 1;
> +
> +    for_each_set_bit ( i, val )
>      {
>          struct vgic_irq *irq;
>          unsigned long flags;
> @@ -182,11 +186,13 @@ void vgic_mmio_write_spending(struct vcpu *vcpu,
>                                unsigned long val)
>  {
>      uint32_t intid = VGIC_ADDR_TO_INTID(addr, 1);
> -    unsigned int i;
>      unsigned long flags;
>      irq_desc_t *desc;
> 
> -    bitmap_for_each ( i, &val, len * 8 )
> +    if ( len < sizeof(val) )
> +        val &= (1UL << (len * 8)) - 1;
> +
> +    for_each_set_bit ( i, val )
>      {
>          struct vgic_irq *irq = vgic_get_irq(vcpu->domain, vcpu, intid + i);
> 
> @@ -230,11 +236,13 @@ void vgic_mmio_write_cpending(struct vcpu *vcpu,
>                                unsigned long val)
>  {
>      uint32_t intid = VGIC_ADDR_TO_INTID(addr, 1);
> -    unsigned int i;
>      unsigned long flags;
>      irq_desc_t *desc;
> 
> -    bitmap_for_each ( i, &val, len * 8 )
> +    if ( len < sizeof(val) )
> +        val &= (1UL << (len * 8)) - 1;
> +
> +    for_each_set_bit ( i, val )
>      {
>          struct vgic_irq *irq = vgic_get_irq(vcpu->domain, vcpu, intid + i);
> 
> @@ -326,9 +334,11 @@ void vgic_mmio_write_cactive(struct vcpu *vcpu,
>                               unsigned long val)
>  {
>      uint32_t intid = VGIC_ADDR_TO_INTID(addr, 1);
> -    unsigned int i;
> 
> -    bitmap_for_each ( i, &val, len * 8 )
> +    if ( len < sizeof(val) )
> +        val &= (1UL << (len * 8)) - 1;
> +
> +    for_each_set_bit ( i, val )
>      {
>          struct vgic_irq *irq = vgic_get_irq(vcpu->domain, vcpu, intid + i);
> 
> @@ -356,9 +366,11 @@ void vgic_mmio_write_sactive(struct vcpu *vcpu,
>                               unsigned long val)
>  {
>      uint32_t intid = VGIC_ADDR_TO_INTID(addr, 1);
> -    unsigned int i;
> 
> -    bitmap_for_each ( i, &val, len * 8 )
> +    if ( len < sizeof(val) )
> +        val &= (1UL << (len * 8)) - 1;
> +
> +    for_each_set_bit ( i, val )
>      {
>          struct vgic_irq *irq = vgic_get_irq(vcpu->domain, vcpu, intid + i);
> 
> --
> 2.39.2
> 

~Michal