On 8/8/25 10:17, Zhao Liu wrote:
(+Hanna: I would like to align with Hanna on 0002.diff patch :-))
On Thu, Aug 07, 2025 at 03:59:26PM +0200, Paolo Bonzini wrote:
Date: Thu, 7 Aug 2025 15:59:26 +0200
From: Paolo Bonzini <pbonz...@redhat.com>
Subject: Re: [RFC 10/26] subprojects/vm-memory: Patch vm-memory for QEMU
memory backend
On 8/7/25 14:30, Zhao Liu wrote:
Add 2 patches to support QEMU memory backend implementation.
Signed-off-by: Zhao Liu <zhao1....@intel.com>
---
.../packagefiles/vm-memory-0.16-rs/0001.diff | 81 +++++++++++++
.../packagefiles/vm-memory-0.16-rs/0002.diff | 111 ++++++++++++++++++
subprojects/vm-memory-0.16-rs.wrap | 2 +
3 files changed, 194 insertions(+)
create mode 100644 subprojects/packagefiles/vm-memory-0.16-rs/0001.diff
create mode 100644 subprojects/packagefiles/vm-memory-0.16-rs/0002.diff
diff --git a/subprojects/packagefiles/vm-memory-0.16-rs/0001.diff
b/subprojects/packagefiles/vm-memory-0.16-rs/0001.diff
new file mode 100644
index 000000000000..037193108d45
--- /dev/null
+++ b/subprojects/packagefiles/vm-memory-0.16-rs/0001.diff
@@ -0,0 +1,81 @@
+From 298f8ba019b2fe159fa943e0ae4dfd3c83ee64e0 Mon Sep 17 00:00:00 2001
+From: Zhao Liu <zhao1....@intel.com>
+Date: Wed, 6 Aug 2025 11:31:11 +0800
+Subject: [PATCH 1/2] guest_memory: Add a marker tarit to implement
+ Bytes<GuestAddress> for GuestMemory
This was a bit surprising. Maybe this is something where GuestMemory needs
some extra flexibility.
At least, the default GuestMemory::try_access() need to re-implement in
QEMU, and this is because GuestMemory::iter() doesn't fit for QEMU's
case, and GuestMemory::to_region_addr() also needs adjustment to support
complete translation.
For details,
1) iter() - QEMU has implemented the two-level "page" walk in
`phys_page_find`, which is more efficient than linear iteration.
2) to_region_addr() - it's function signature is:
fn to_region_addr(
&self,
addr: GuestAddress
) -> Option<(&Self::R, MemoryRegionAddress)>;
but QEMU currentlt wants:
fn translate(
&self,
addr: GuestAddress,
len: GuestUsize,
is_write: bool,
) -> Option<(&MemoryRegionSection, MemoryRegionAddress, GuestUsize)>
`is_write` is mainly about IOMMU (and read-only case, but that could be
workaround I think).
And the 3rd member `GuestUsize` of (&MemoryRegionSection,
MemoryRegionAddress, GuestUsize) indicates the remianing size, which is
used to detect cross-region case. Maybe this `GuestUsize` is not
necessary in its return, since we can check the size of `MemoryRegionSection`
later. But this would be a bit repetitive.
But at least, this marker trait is acceptable, right? :-)
The marker trait for GuestMemoryRegion is introduced at commit 66ff347
("refactor: use matches! instead of to_string() for tests").
@@ -0,0 +1,111 @@
+From 2af7ea12a589fde619690e5060c01710cb6f2e0e Mon Sep 17 00:00:00 2001
+From: Zhao Liu <zhao1....@intel.com>
+Date: Wed, 6 Aug 2025 14:27:14 +0800
+Subject: [PATCH 2/2] guest_memory: Add is_write argument for
+ GuestMemory::try_access()
This should be fine. But Hanna is also working on IOMMU so maybe this won't
be needed!
I'm not sure what method could align with Hanna's design. If there's
another interface/method, I can have a try.
For example she already has similar fixes in
https://github.com/rust-vmm/vm-memory/pull/327:
https://github.com/rust-vmm/vm-memory/pull/327/commits/9bcd5ac9b9ae37d1fb421f86f0aff310411933af
Bytes: Fix read() and write()
read() and write() must not ignore the `count` parameter: The
mappings passed into the `try_access()` closure are only valid for up
to `count` bytes, not more.
https://github.com/rust-vmm/vm-memory/pull/327/commits/2b83c72be656e5d46b83cb3a66d580e56cf33d5b
Bytes: Do not use to_region_addr()
When we switch to a (potentially) virtual memory model [...]
the one memory-region-referencing part we are going to keep is
`try_access()` [...] switch `Bytes::load()` and `store()` from using
`to_region_addr()` to `try_access()`.
With some luck, your custom implementation of Bytes<GuestAddress> is not
needed once vm-memory supports iommu.
Paolo
