On 2018/5/24 22:56, Peter Maydell wrote: > On 24 May 2018 at 15:40, Auger Eric <eric.au...@redhat.com> wrote: >> > Hi Peter, >> > >> > On 05/24/2018 04:16 PM, Peter Maydell wrote: >>> >> Only for KVM, not for TCG, and it's the other way round: we >>> >> end up with two lots of PPI/SGI space in the data structure >>> >> by mistake. Let me fish out the comment I made on the v2 of this >>> >> series: >>> >> >>> >> In the code in master, we have QEMU data structures >>> >> (bitmaps, etc) which have one entry for each of GICV3_MAXIRQ >>> >> irqs. That includes the RAZ/WI unused space for the SPIs/PPIs, so >>> >> for a 1-bit-per-irq bitmap: >>> >> [0x00000000, irq 32, irq 33, .... ] >>> >> >>> >> When we fill in the values from KVM into these data structures, >>> >> we start after the unused space, because the for_each_dist_irq_reg() >>> >> macro starts with _irq = GIC_INTERNAL. But we forgot to adjust >>> >> the offset value we use for the KVM access, so we start by >>> >> reading the RAZ/WI values from KVM, and the data structure >>> >> contents end up with: >>> >> [0x00000000, 0x00000000, irq 32, irq 33, ... ] >>> >> (and the last irqs wouldn't get transferred). >> > In kvm_dist_get_priority (new code), the offset is where we read and >> > field is where we write, correct? Offset was shifted so we effectively >> > read in KVM regs the num_irq-32 SPI states now but don't we start >> > writing at the beginning of bmp, (ie s->gicd_ipriority), at PPI/SGI >> > offset? What am I missing? > Oops, yes, you're right. My explanation applies to the > various other bitmaps, where we are accessing the > fields in the data structure using gic_bmp_ptr32(bmp, irq), > but not to gicd_ipriority[], which we are directly accessing > starting with the first word, not by indexing via bmp[irq]. > > So we need to handle these two cases differently. > You're correct that for gicd_ipriority[], the code in > master reads and writes to that data structure as: > [0, 0, ..., 0, irq 32, irq 33, ..., 0, 0, ... 0] > so all the values are in the right place but we: > (a) unnecessarily read/write zeroes for the PPI/SGI fields > (b) fail to transfer the last 32 interrupts > > We can fix the gicd_ipriority[] case simply by adding > bmp = GIC_INTERNAL; > before the assignment to 'field' in both kvm_dist_get_priority() > and kvm_dist_put_priority(). This doesn't affect migration > compatibility. We should do this separately from fixing the > other bitmaps, because it's simpler. > If we do bmp += GIC_INTERNAL, we should also add this to offset, otherwise we will put the SGI/PPIs data to SPIs, right?
Thanks, -- Shannon
