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([2a01:e0a:59e:9d80:527b:9dff:feef:3874]) by smtp.gmail.com with ESMTPSA id p22-20020ac84616000000b0031ea864d3b2sm10496340qtn.30.2022.08.03.01.44.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 03 Aug 2022 01:44:50 -0700 (PDT) Message-ID: <3db8b274-dfe6-7b68-0ef3-d72c3597dd10@redhat.com> Date: Wed, 3 Aug 2022 10:44:46 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH 1/2] hw/arm/virt: Improve address assignment for highmem IO regions Content-Language: en-US To: Gavin Shan , qemu-arm@nongnu.org Cc: qemu-devel@nongnu.org, peter.maydell@linaro.org, richard.henderson@linaro.org, cohuck@redhat.com, zhenyzha@redhat.com, shan.gavin@gmail.com, Marc Zyngier References: <20220802064529.547361-1-gshan@redhat.com> <20220802064529.547361-2-gshan@redhat.com> <9c8365c6-d27b-df76-371d-bd32ca2a26f7@redhat.com> From: Eric Auger In-Reply-To: <9c8365c6-d27b-df76-371d-bd32ca2a26f7@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=eric.auger@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: eric.auger@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi Gavin, On 8/3/22 05:01, Gavin Shan wrote: > Hi Eric, > > On 8/2/22 7:41 PM, Eric Auger wrote: >> On 8/2/22 08:45, Gavin Shan wrote: >>> There are 3 highmem IO regions as below. They can be disabled in >>> two situations: (a) The specific region is disabled by user. (b) >>> The specific region doesn't fit in the PA space. However, the base >>> address and highest_gpa are still updated no matter if the region >>> is enabled or disabled. It's incorrectly incurring waste in the PA >>> space. >> If I am not wrong highmem_redists and highmem_mmio are not user >> selectable >> >> Only highmem ecam depends on machine type & ACPI setup. But I would say >> that in server use case it is always set. So is that optimization really >> needed? > > There are two other cases you missed. > > - highmem_ecam is enabled after virt-2.12, meaning it stays disabled >   before that. Yes that's what I meant above by 'depends on machine type' > > - The high memory region can be disabled if user is asking large >   (normal) memory space through 'maxmem=' option. When the requested >   memory by 'maxmem=' is large enough, the high memory regions are >   disabled. It means the normal memory has higher priority than those >   high memory regions. This is the case I provided in (b) of the >   commit log. yes but in such a case you don't "waste" IPA as you mention in the commit log because you only ask for a VM dimensionned for the highest_gpa. The only case where you would "waste" IPA is for high ecam which can disabled by option combination but it is marginal. > > In the commit log, I was supposed to say something like below for > (a): > > - The specific high memory region can be disabled through changing >   the code by user or developer. For example, 'vms->highmem_mmio' >   is changed from true to false in virt_instance_init(). > >>> >>> Improve address assignment for highmem IO regions to avoid the waste >>> in the PA space by putting the logic into virt_memmap_fits(). >>> >>> Signed-off-by: Gavin Shan >>> --- >>>   hw/arm/virt.c | 54 >>> +++++++++++++++++++++++++++++---------------------- >>>   1 file changed, 31 insertions(+), 23 deletions(-) >>> >>> diff --git a/hw/arm/virt.c b/hw/arm/virt.c >>> index 9633f822f3..bc0cd218f9 100644 >>> --- a/hw/arm/virt.c >>> +++ b/hw/arm/virt.c >>> @@ -1688,6 +1688,34 @@ static uint64_t >>> virt_cpu_mp_affinity(VirtMachineState *vms, int idx) >>>       return arm_cpu_mp_affinity(idx, clustersz); >>>   } >>>   +static void virt_memmap_fits(VirtMachineState *vms, int index, >>> +                             bool *enabled, hwaddr *base, int pa_bits) >>> +{ >>> +    hwaddr size = extended_memmap[index].size; >>> + >>> +    /* The region will be disabled if its size isn't given */ >>> +    if (!*enabled || !size) { >> In which case do you have !size? > > Yeah, we don't have !size and the condition should be removed. > >>> +        *enabled = false; >>> +        vms->memmap[index].base = 0; >>> +        vms->memmap[index].size = 0; >> It looks dangerous to me to reset the region's base and size like that. >> for instance fdt_add_gic_node() will add dummy data in the dt. > > I would guess you missed that the high memory regions won't be exported > through device-tree if they have been disabled. We have a check there, > which is "if (nb_redist_regions == 1)" OK I missed a check was added in virt_gicv3_redist_region_count. Nevertheless, your comment "The region will be disabled if its size isn't given */ is not obvious to me. To me the region is disabled if the corresponding flag is not set. From your comment I have the impression the size is checked to see if the region is exposed, it does not look obvious. > >>> +        return; >>> +    } >>> + >>> +    /* >>> +     * Check if the memory region fits in the PA space. The memory map >>> +     * and highest_gpa are updated if it fits. Otherwise, it's >>> disabled. >>> +     */ >>> +    *enabled = (ROUND_UP(*base, size) + size <= BIT_ULL(pa_bits)); >> using a 'fits' local variable would make the code more obvious I think > > Lets confirm if you're suggesting something like below? > >         bool fits; > >         fits = (ROUND_UP(*base, size) + size <= BIT_ULL(pa_bits)); > >         if (fits) { >            /* update *base, memory mapping, highest_gpa */ >         } else { >            *enabled = false; >         } yes that's what I suggested. > > I guess we can simply do > >         if (ROUND_UP(*base, size) + size <= BIT_ULL(pa_bits)) { >            /* update *base, memory mapping, highest_gpa */ >         } else { >            *enabled = false; >         } > > Please let me know which one looks best to you. > >>> +    if (*enabled) { >>> +        *base = ROUND_UP(*base, size); >>> +        vms->memmap[index].base = *base; >>> +        vms->memmap[index].size = size; >>> +        vms->highest_gpa = *base + size - 1; >>> + >>> +    *base = *base + size; >>> +    } >>> +} >>> + >>>   static void virt_set_memmap(VirtMachineState *vms, int pa_bits) >>>   { >>>       MachineState *ms = MACHINE(vms); >>> @@ -1744,37 +1772,17 @@ static void virt_set_memmap(VirtMachineState >>> *vms, int pa_bits) >>>       vms->highest_gpa = memtop - 1; >>>         for (i = VIRT_LOWMEMMAP_LAST; i < >>> ARRAY_SIZE(extended_memmap); i++) { >>> -        hwaddr size = extended_memmap[i].size; >>> -        bool fits; >>> - >>> -        base = ROUND_UP(base, size); >>> -        vms->memmap[i].base = base; >>> -        vms->memmap[i].size = size; >>> - >>> -        /* >>> -         * Check each device to see if they fit in the PA space, >>> -         * moving highest_gpa as we go. >>> -         * >>> -         * For each device that doesn't fit, disable it. >>> -         */ >>> -        fits = (base + size) <= BIT_ULL(pa_bits); >>> -        if (fits) { >>> -            vms->highest_gpa = base + size - 1; >>> -        } >>> - >> >> we could avoid running the code below in case highmem is not set. We >> would need to reset that flags though. >> > > Yeah, I think it's not a big deal. My though is to update the flag in > virt_memmap_fits(). Eric > >>>           switch (i) { >>>           case VIRT_HIGH_GIC_REDIST2: >>> -            vms->highmem_redists &= fits; >>> +            virt_memmap_fits(vms, i, &vms->highmem_redists, &base, >>> pa_bits); >>>               break; >>>           case VIRT_HIGH_PCIE_ECAM: >>> -            vms->highmem_ecam &= fits; >>> +            virt_memmap_fits(vms, i, &vms->highmem_ecam, &base, >>> pa_bits); >>>               break; >>>           case VIRT_HIGH_PCIE_MMIO: >>> -            vms->highmem_mmio &= fits; >>> +            virt_memmap_fits(vms, i, &vms->highmem_mmio, &base, >>> pa_bits); >>>               break; >>>           } >>> - >>> -        base += size; >>>       } >>>         if (device_memory_size > 0) { > > Thanks, > Gavin >