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[for-10.0] docs: Document removal of 64-bit on 32-bit emulation

Message ID 20250412164315.36161-1-richard.henderson@linaro.org
State New
Headers show
Series [for-10.0] docs: Document removal of 64-bit on 32-bit emulation | expand

Commit Message

Richard Henderson April 12, 2025, 4:43 p.m. UTC 
With acce728cbc6c we disallowed configuring 64-bit guests on
32-bit hosts, but forgot to document that in removed-features.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 docs/about/removed-features.rst | 9 +++++++++
 1 file changed, 9 insertions(+)
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Patch

diff --git a/docs/about/removed-features.rst b/docs/about/removed-features.rst
index 2527a91795..790a5e481c 100644
--- a/docs/about/removed-features.rst
+++ b/docs/about/removed-features.rst
@@ -858,6 +858,15 @@  QEMU.  Since all recent x86 hardware from the past >10 years is
 capable of the 64-bit x86 extensions, a corresponding 64-bit OS should
 be used instead.
 
+32-bit hosts for 64-bit guests (removed in 10.0)
+''''''''''''''''''''''''''''''''''''''''''''''''
+
+In general, 32-bit hosts cannot support the memory space or atomicity
+requirements of 64-bit guests.  Prior to 10.0, QEMU attempted to
+work around the atomicity issues in system mode by running all vCPUs
+in a single thread context; in user mode atomicity was simply broken.
+From 10.0, QEMU has disabled configuration of 64-bit guests on 32-bit hosts.
+
 Guest Emulator ISAs
 -------------------