On 1/8/2025 12:47 PM, Alexey Kardashevskiy wrote:
> On 13/12/24 18:08, Chenyi Qiang wrote:
>> Introduce the realize()/unrealize() callbacks to initialize/uninitialize
>> the new guest_memfd_manager object and register/unregister it in the
>> target MemoryRegion.
>>
>> Guest_memfd was initially set to shared until the commit bd3bcf6962
>> ("kvm/memory: Make memory type private by default if it has guest memfd
>> backend"). To align with this change, the default state in
>> guest_memfd_manager is set to private. (The bitmap is cleared to 0).
>> Additionally, setting the default to private can also reduce the
>> overhead of mapping shared pages into IOMMU by VFIO during the bootup
>> stage.
>>
>> Signed-off-by: Chenyi Qiang <chenyi.qiang@xxxxxxxxx>
>> ---
>> include/sysemu/guest-memfd-manager.h | 27 +++++++++++++++++++++++++++
>> system/guest-memfd-manager.c | 28 +++++++++++++++++++++++++++-
>> system/physmem.c | 7 +++++++
>> 3 files changed, 61 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/sysemu/guest-memfd-manager.h b/include/sysemu/
>> guest-memfd-manager.h
>> index 9dc4e0346d..d1e7f698e8 100644
>> --- a/include/sysemu/guest-memfd-manager.h
>> +++ b/include/sysemu/guest-memfd-manager.h
>> @@ -42,6 +42,8 @@ struct GuestMemfdManager {
>> struct GuestMemfdManagerClass {
>> ObjectClass parent_class;
>> + void (*realize)(GuestMemfdManager *gmm, MemoryRegion *mr,
>> uint64_t region_size);
>> + void (*unrealize)(GuestMemfdManager *gmm);
>> int (*state_change)(GuestMemfdManager *gmm, uint64_t offset,
>> uint64_t size,
>> bool shared_to_private);
>> };
>> @@ -61,4 +63,29 @@ static inline int
>> guest_memfd_manager_state_change(GuestMemfdManager *gmm, uint6
>> return 0;
>> }
>> +static inline void guest_memfd_manager_realize(GuestMemfdManager *gmm,
>> + MemoryRegion *mr,
>> uint64_t region_size)
>> +{
>> + GuestMemfdManagerClass *klass;
>> +
>> + g_assert(gmm);
>> + klass = GUEST_MEMFD_MANAGER_GET_CLASS(gmm);
>> +
>> + if (klass->realize) {
>> + klass->realize(gmm, mr, region_size);
>
> Ditch realize() hook and call guest_memfd_manager_realizefn() directly?
> Not clear why these new hooks are needed.
>
>> + }
>> +}
>> +
>> +static inline void guest_memfd_manager_unrealize(GuestMemfdManager *gmm)
>> +{
>> + GuestMemfdManagerClass *klass;
>> +
>> + g_assert(gmm);
>> + klass = GUEST_MEMFD_MANAGER_GET_CLASS(gmm);
>> +
>> + if (klass->unrealize) {
>> + klass->unrealize(gmm);
>> + }
>> +}
>
> guest_memfd_manager_unrealizefn()?
Agree. Adding these wrappers seem unnecessary.
>
>
>> +
>> #endif
>> diff --git a/system/guest-memfd-manager.c b/system/guest-memfd-manager.c
>> index 6601df5f3f..b6a32f0bfb 100644
>> --- a/system/guest-memfd-manager.c
>> +++ b/system/guest-memfd-manager.c
>> @@ -366,6 +366,31 @@ static int
>> guest_memfd_state_change(GuestMemfdManager *gmm, uint64_t offset,
>> return ret;
>> }
>> +static void guest_memfd_manager_realizefn(GuestMemfdManager *gmm,
>> MemoryRegion *mr,
>> + uint64_t region_size)
>> +{
>> + uint64_t bitmap_size;
>> +
>> + gmm->block_size = qemu_real_host_page_size();
>> + bitmap_size = ROUND_UP(region_size, gmm->block_size) / gmm-
>> >block_size;
>
> imho unaligned region_size should be an assert.
There's no guarantee the region_size of the MemoryRegion is PAGE_SIZE
aligned. So the ROUND_UP() is more appropriate.
>
>> +
>> + gmm->mr = mr;
>> + gmm->bitmap_size = bitmap_size;
>> + gmm->bitmap = bitmap_new(bitmap_size);
>> +
>> + memory_region_set_ram_discard_manager(gmm->mr,
>> RAM_DISCARD_MANAGER(gmm));
>> +}
>
> This belongs to 2/7.
>
>> +
>> +static void guest_memfd_manager_unrealizefn(GuestMemfdManager *gmm)
>> +{
>> + memory_region_set_ram_discard_manager(gmm->mr, NULL);
>> +
>> + g_free(gmm->bitmap);
>> + gmm->bitmap = NULL;
>> + gmm->bitmap_size = 0;
>> + gmm->mr = NULL;
>
> @gmm is being destroyed here, why bother zeroing?
OK, will remove it.
>
>> +}
>> +
>
> This function belongs to 2/7.
Will move both realizefn() and unrealizefn().
>
>> static void guest_memfd_manager_init(Object *obj)
>> {
>> GuestMemfdManager *gmm = GUEST_MEMFD_MANAGER(obj);
>> @@ -375,7 +400,6 @@ static void guest_memfd_manager_init(Object *obj)
>> static void guest_memfd_manager_finalize(Object *obj)
>> {
>> - g_free(GUEST_MEMFD_MANAGER(obj)->bitmap);
>> }
>> static void guest_memfd_manager_class_init(ObjectClass *oc, void
>> *data)
>> @@ -384,6 +408,8 @@ static void
>> guest_memfd_manager_class_init(ObjectClass *oc, void *data)
>> RamDiscardManagerClass *rdmc = RAM_DISCARD_MANAGER_CLASS(oc);
>> gmmc->state_change = guest_memfd_state_change;
>> + gmmc->realize = guest_memfd_manager_realizefn;
>> + gmmc->unrealize = guest_memfd_manager_unrealizefn;
>> rdmc->get_min_granularity = guest_memfd_rdm_get_min_granularity;
>> rdmc->register_listener = guest_memfd_rdm_register_listener;
>> diff --git a/system/physmem.c b/system/physmem.c
>> index dc1db3a384..532182a6dd 100644
>> --- a/system/physmem.c
>> +++ b/system/physmem.c
>> @@ -53,6 +53,7 @@
>> #include "sysemu/hostmem.h"
>> #include "sysemu/hw_accel.h"
>> #include "sysemu/xen-mapcache.h"
>> +#include "sysemu/guest-memfd-manager.h"
>> #include "trace.h"
>> #ifdef CONFIG_FALLOCATE_PUNCH_HOLE
>> @@ -1885,6 +1886,9 @@ static void ram_block_add(RAMBlock *new_block,
>> Error **errp)
>> qemu_mutex_unlock_ramlist();
>> goto out_free;
>> }
>> +
>> + GuestMemfdManager *gmm =
>> GUEST_MEMFD_MANAGER(object_new(TYPE_GUEST_MEMFD_MANAGER));
>> + guest_memfd_manager_realize(gmm, new_block->mr, new_block-
>> >mr->size);
>
> Wow. Quite invasive.
Yeah... It creates a manager object no matter whether the user wants to
use shared passthru or not. We assume some fields like private/shared
bitmap may also be helpful in other scenario for future usage, and if no
passthru device, the listener would just return, so it is acceptable.
>
>> }
>> ram_size = (new_block->offset + new_block->max_length) >>
>> TARGET_PAGE_BITS;
>> @@ -2139,6 +2143,9 @@ static void reclaim_ramblock(RAMBlock *block)
>> if (block->guest_memfd >= 0) {
>> close(block->guest_memfd);
>> + GuestMemfdManager *gmm = GUEST_MEMFD_MANAGER(block->mr->rdm);
>> + guest_memfd_manager_unrealize(gmm);
>> + object_unref(OBJECT(gmm));
>
> Likely don't matter but I'd do the cleanup before close() or do block-
>>guest_memfd=-1 before the cleanup. Thanks,
>
>
>> ram_block_discard_require(false);
>> }
>>
>
