From 8d8fd49920c7b4c49d2d7ca1666c3cc7a53a3e96 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Fri, 18 Jul 2025 18:11:28 +0200 Subject: [PATCH 115/115] physmem: Support coordinated discarding of RAM with guest_memfd RH-Author: Paolo Bonzini RH-MergeRequest: 391: TDX support, including attestation and device assignment RH-Jira: RHEL-15710 RHEL-20798 RHEL-49728 RH-Acked-by: Yash Mankad RH-Acked-by: Peter Xu RH-Acked-by: David Hildenbrand RH-Commit: [115/115] 5dfe5036d7b5524f0d0af4cde23cdd9ca696717b (bonzini/rhel-qemu-kvm) A new field, attributes, was introduced in RAMBlock to link to a RamBlockAttributes object, which centralizes all guest_memfd related information (such as fd and status bitmap) within a RAMBlock. Create and initialize the RamBlockAttributes object upon ram_block_add(). Meanwhile, register the object in the target RAMBlock's MemoryRegion. After that, guest_memfd-backed RAMBlock is associated with the RamDiscardManager interface, and the users can execute RamDiscardManager specific handling. For example, VFIO will register the RamDiscardListener and get notifications when the state_change() helper invokes. As coordinate discarding of RAM with guest_memfd is now supported, only block uncoordinated discard. Tested-by: Alexey Kardashevskiy Reviewed-by: Alexey Kardashevskiy Acked-by: David Hildenbrand Signed-off-by: Chenyi Qiang Link: https://lore.kernel.org/r/20250612082747.51539-6-chenyi.qiang@intel.com Signed-off-by: Peter Xu (cherry picked from commit 2fde3fb916079ee0ff0fc26d9446c813b1d5cc28) Signed-off-by: Paolo Bonzini Conflicts: No CPR --- accel/kvm/kvm-all.c | 9 +++++++++ include/exec/ramblock.h | 1 + system/physmem.c | 23 +++++++++++++++++++++-- 3 files changed, 31 insertions(+), 2 deletions(-) diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c index 43c10c82f6..1fd7773a28 100644 --- a/accel/kvm/kvm-all.c +++ b/accel/kvm/kvm-all.c @@ -3073,6 +3073,15 @@ int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private) addr = memory_region_get_ram_ptr(mr) + section.offset_within_region; rb = qemu_ram_block_from_host(addr, false, &offset); + ret = ram_block_attributes_state_change(RAM_BLOCK_ATTRIBUTES(mr->rdm), + offset, size, to_private); + if (ret) { + error_report("Failed to notify the listener the state change of " + "(0x%"HWADDR_PRIx" + 0x%"HWADDR_PRIx") to %s", + start, size, to_private ? "private" : "shared"); + goto out_unref; + } + if (to_private) { if (rb->page_size != qemu_real_host_page_size()) { /* diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h index 9ae774d268..a504765038 100644 --- a/include/exec/ramblock.h +++ b/include/exec/ramblock.h @@ -46,6 +46,7 @@ struct RAMBlock { int fd; uint64_t fd_offset; int guest_memfd; + RamBlockAttributes *attributes; size_t page_size; /* dirty bitmap used during migration */ unsigned long *bmap; diff --git a/system/physmem.c b/system/physmem.c index dccc95030b..35f8f25e22 100644 --- a/system/physmem.c +++ b/system/physmem.c @@ -1889,7 +1889,7 @@ static void ram_block_add(RAMBlock *new_block, Error **errp) } assert(new_block->guest_memfd < 0); - ret = ram_block_discard_require(true); + ret = ram_block_coordinated_discard_require(true); if (ret < 0) { error_setg_errno(errp, -ret, "cannot set up private guest memory: discard currently blocked"); @@ -1903,6 +1903,24 @@ static void ram_block_add(RAMBlock *new_block, Error **errp) qemu_mutex_unlock_ramlist(); goto out_free; } + + /* + * The attribute bitmap of the RamBlockAttributes is default to + * discarded, which mimics the behavior of kvm_set_phys_mem() when it + * calls kvm_set_memory_attributes_private(). This leads to a brief + * period of inconsistency between the creation of the RAMBlock and its + * mapping into the physical address space. However, this is not + * problematic, as no users rely on the attribute status to perform + * any actions during this interval. + */ + new_block->attributes = ram_block_attributes_create(new_block); + if (!new_block->attributes) { + error_setg(errp, "Failed to create ram block attribute"); + close(new_block->guest_memfd); + ram_block_coordinated_discard_require(false); + qemu_mutex_unlock_ramlist(); + goto out_free; + } } new_ram_size = MAX(old_ram_size, @@ -2159,8 +2177,9 @@ static void reclaim_ramblock(RAMBlock *block) } if (block->guest_memfd >= 0) { + ram_block_attributes_destroy(block->attributes); close(block->guest_memfd); - ram_block_discard_require(false); + ram_block_coordinated_discard_require(false); } g_free(block); -- 2.50.1