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authorChristian Krinitsin <mail@krinitsin.com>2025-07-03 07:27:52 +0000
committerChristian Krinitsin <mail@krinitsin.com>2025-07-03 07:27:52 +0000
commitd0c85e36e4de67af628d54e9ab577cc3fad7796a (patch)
treef8f784b0f04343b90516a338d6df81df3a85dfa2 /results/classifier/gemma3:12b/hypervisor/1211910
parent7f4364274750eb8cb39a3e7493132fca1c01232e (diff)
downloademulator-bug-study-d0c85e36e4de67af628d54e9ab577cc3fad7796a.tar.gz
emulator-bug-study-d0c85e36e4de67af628d54e9ab577cc3fad7796a.zip
add deepseek and gemma results
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+Logical to linear address translation is wrong for 32-bit guests on a 64-bit hypervisor
+
+I run a 64-bit hypervisor in qemu-system-x86_64 (without KVM) and on top of that I have a 32-bit guest. The guest configures the code-segment to have a base of 0x4000_0000 and a limit of 0xFFFF_FFFF with paging disabled. Thus, if a logical address of e.g. 0xC000_0000 is used, it should be translated to 0x0000_0000 (linear and physical), because of the overflow that happens.
+But this does not happen with the described setup. Instead, qemu seems to calculate the logical to linear translation with 64-bit addresses so that no overflow happens. Consequently, the resulting address is 0x1_0000_0000 and this gets written to exitinfo2 in the VMCB structure. This causes trouble for hypervisors that expect the upper 32 bits of exitinfo2 to be 0 for 32-bit guests.
+
+Note also that the exact same setup runs fine on real AMD machines with SVM. That is, the upper 32 bits in exitinfo2 are always 0 because of the overflow.
+
+I've tested that with the latest development version of QEMU (commit 328465fd9f3a628ab320b5959d68d3d49df58fa6).
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