Re: [PATCH 1/7] memory: Export a helper to get intersection of a MemoryRegionSection with a given range

David Hildenbrand
2025-01-20T12:50:49Z

On 08.01.25 05:47, Alexey Kardashevskiy wrote:
> On 13/12/24 18:08, Chenyi Qiang wrote:
>> Rename the helper to memory_region_section_intersect_range() to make it
>> more generic.
>>
>> Signed-off-by: Chenyi Qiang <chenyi.qiang@intel.com>
>> ---
>> hw/virtio/virtio-mem.c | 32 +++++---------------------------
>> include/exec/memory.h | 13 +++++++++++++
>> system/memory.c | 17 +++++++++++++++++
>> 3 files changed, 35 insertions(+), 27 deletions(-)
>>
>> diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
>> index 80ada89551..e3d1ccaeeb 100644
>> --- a/hw/virtio/virtio-mem.c
>> +++ b/hw/virtio/virtio-mem.c
>> @@ -242,28 +242,6 @@ static int virtio_mem_for_each_plugged_range(VirtIOMEM *vmem, void *arg,
>> return ret;
>> }
>>
>> -/*
>> - * Adjust the memory section to cover the intersection with the given range.
>> - *
>> - * Returns false if the intersection is empty, otherwise returns true.
>> - */
>> -static bool virtio_mem_intersect_memory_section(MemoryRegionSection *s,
>> - uint64_t offset, uint64_t size)
>> -{
>> - uint64_t start = MAX(s->offset_within_region, offset);
>> - uint64_t end = MIN(s->offset_within_region + int128_get64(s->size),
>> - offset + size);
>> -
>> - if (end <= start) {
>> - return false;
>> - }
>> -
>> - s->offset_within_address_space += start - s->offset_within_region;
>> - s->offset_within_region = start;
>> - s->size = int128_make64(end - start);
>> - return true;
>> -}
>> -
>> typedef int (*virtio_mem_section_cb)(MemoryRegionSection *s, void *arg);
>>
>> static int virtio_mem_for_each_plugged_section(const VirtIOMEM *vmem,
>> @@ -285,7 +263,7 @@ static int virtio_mem_for_each_plugged_section(const VirtIOMEM *vmem,
>> first_bit + 1) - 1;
>> size = (last_bit - first_bit + 1) * vmem->block_size;
>>
>> - if (!virtio_mem_intersect_memory_section(&tmp, offset, size)) {
>> + if (!memory_region_section_intersect_range(&tmp, offset, size)) {
>> break;
>> }
>> ret = cb(&tmp, arg);
>> @@ -317,7 +295,7 @@ static int virtio_mem_for_each_unplugged_section(const VirtIOMEM *vmem,
>> first_bit + 1) - 1;
>> size = (last_bit - first_bit + 1) * vmem->block_size;
>>
>> - if (!virtio_mem_intersect_memory_section(&tmp, offset, size)) {
>> + if (!memory_region_section_intersect_range(&tmp, offset, size)) {
>> break;
>> }
>> ret = cb(&tmp, arg);
>> @@ -353,7 +331,7 @@ static void virtio_mem_notify_unplug(VirtIOMEM *vmem, uint64_t offset,
>> QLIST_FOREACH(rdl, &vmem->rdl_list, next) {
>> MemoryRegionSection tmp = *rdl->section;
>>
>> - if (!virtio_mem_intersect_memory_section(&tmp, offset, size)) {
>> + if (!memory_region_section_intersect_range(&tmp, offset, size)) {
>> continue;
>> }
>> rdl->notify_discard(rdl, &tmp);
>> @@ -369,7 +347,7 @@ static int virtio_mem_notify_plug(VirtIOMEM *vmem, uint64_t offset,
>> QLIST_FOREACH(rdl, &vmem->rdl_list, next) {
>> MemoryRegionSection tmp = *rdl->section;
>>
>> - if (!virtio_mem_intersect_memory_section(&tmp, offset, size)) {
>> + if (!memory_region_section_intersect_range(&tmp, offset, size)) {
>> continue;
>> }
>> ret = rdl->notify_populate(rdl, &tmp);
>> @@ -386,7 +364,7 @@ static int virtio_mem_notify_plug(VirtIOMEM *vmem, uint64_t offset,
>> if (rdl2 == rdl) {
>> break;
>> }
>> - if (!virtio_mem_intersect_memory_section(&tmp, offset, size)) {
>> + if (!memory_region_section_intersect_range(&tmp, offset, size)) {
>> continue;
>> }
>> rdl2->notify_discard(rdl2, &tmp);
>> diff --git a/include/exec/memory.h b/include/exec/memory.h
>> index e5e865d1a9..ec7bc641e8 100644
>> --- a/include/exec/memory.h
>> +++ b/include/exec/memory.h
>> @@ -1196,6 +1196,19 @@ MemoryRegionSection *memory_region_section_new_copy(MemoryRegionSection *s);
>> */
>> void memory_region_section_free_copy(MemoryRegionSection *s);
>>
>> +/**
>> + * memory_region_section_intersect_range: Adjust the memory section to cover
>> + * the intersection with the given range.
>> + *
>> + * @s: the #MemoryRegionSection to be adjusted
>> + * @offset: the offset of the given range in the memory region
>> + * @size: the size of the given range
>> + *
>> + * Returns false if the intersection is empty, otherwise returns true.
>> + */
>> +bool memory_region_section_intersect_range(MemoryRegionSection *s,
>> + uint64_t offset, uint64_t size);
>> +
>> /**
>> * memory_region_init: Initialize a memory region
>> *
>> diff --git a/system/memory.c b/system/memory.c
>> index 85f6834cb3..ddcec90f5e 100644
>> --- a/system/memory.c
>> +++ b/system/memory.c
>> @@ -2898,6 +2898,23 @@ void memory_region_section_free_copy(MemoryRegionSection *s)
>> g_free(s);
>> }
>>
>> +bool memory_region_section_intersect_range(MemoryRegionSection *s,
>> + uint64_t offset, uint64_t size)
>> +{
>> + uint64_t start = MAX(s->offset_within_region, offset);
>> + uint64_t end = MIN(s->offset_within_region + int128_get64(s->size),
>> + offset + size);
>
> imho @end needs to be Int128 and s/MIN/int128_min/, etc to be totally
> correct (although it is going to look horrendous). May be it was alright
> when it was just virtio but now it is a wider API.

Yes, virtio-mem operates on RAM regions only, so it does not exceed 64bit.

I understand this is
> cut-n-paste and unlikely scenario of offset+size crossing 1<<64 but
> still.

It's been bugging me for a while that size is 128bit
butoffset_within_address_space and friends are 64bit. Likely we'll never
get offset+size > 64bit here as of now, but it is indeed cleaner to just
handle it using the correct type.

--
Cheers,

David / dhildenb