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We > were able to reproduce this with host kernels 6.13.2 and 6.18.3 on Milan/Genoa > hosts. > > We traced the commit that started causing boot issues to > 68a501d7fd82454525797971c6a0005ceeb93153 and noticed that for some reason the > variable snp_vmpl was non-zero, even though our stack doesn’t run SVSM. This > triggers the sev_es_terminate() call and subsequently crashes the CVM. We > noticed that the commit removes a supposedly redundant rmpadjust() check, but > from our observations it seems that the failed rmpadjust() short-circuited the > check and avoided the underlying issue. > > I was chatting with Tom about this, and taking a deeper look at the issue, we > suspect that the BSS is cleared after the sev_enable() call in > arch/x86/boot/compressed/head_64.S, and that because of this snp_vmpl contains > random junk and is not zeroed. When coming through UEFI, it seems that the BSS > is cleared via drivers/firmware/efi/libstub/x86-stub.c, but in a non-UEFI > bootloader there is no call to startup_64 and so this path is never invoked, > leaving whatever random data was in bss to remain. > > Perhaps the proper fix for this is to put the variables that are set as part of > sev_enable() into .data so that both non-UEFI and UEFI bootloaders will have the > same treatment from the kernel, but I would love to hear everyone’s thoughts on > this. > > Thanks, > Kevin