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Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ] >>>> >>>> On Mon, 20 Apr 2026 08:42:02 +0000 Vasant Hegde wrote: >>>> >>>>> This series addresses CVE-2023-20585 [1] by increasing the AMD IOMMU >>>>> Event log and PPR log buffer sizes to the maximum supported value (512K) >>>>> on affected CPU families when SNP is enabled. >>>>> >>>>> Use MAX buffer size when SNP is enabled on Milan/Genoa. Impacted buffers: >>>>> - Milan : Event log (PPR/GALog is not supported when SNP is enabled) >>>>> - Genoa : Event and PPR log (GALog is not supported when SNP is enabled) >>>>> >>>> >>>> Hi, >>>> >>>> This series seems to break kexec in our production on Milan hosts with SEV enabled. >>>> This is on the 6.18.43 stable kernel backport. >>> >>> Do you have dmesg? >>> >>>> >>>> If on top of 6.18.43 release, we revert the 2 commits, i.e. >>>> Revert "iommu/amd: Use maximum PPR log buffer size when SNP is enabled on Family 0x19" >>>> Revert "iommu/amd: Use maximum Event log buffer size when SNP is enabled on Family 0x19" >>>> >>>> kexec starts working again. >>>>> Could you help in fixing this issue? >>> >>> Sure. We will try to reproduce it internally and get back to you. >> >> Hi, >> >> Just following up, were you able to reproduce this? > > So far no luck with SEV and SEV/SNP. > >> >> I was able to trace down the hang to this do while loop [1]. > > In allocation path, we explicitly set 4K pages (iommu_alloc_4k_pages()). > > If SNP is enabled in host, then in shutdown path, amd_iommu_snp_disable() gets > called and it tries to mark event log memory as shared. In this path, it calls > rmpupdate. But I can't think of reason for it to hang in the rmpupdate loop. > > @Tom, Ashish, Any idea? Not knowing what the physical address is or what the RMP state is, I would have to speculate a bit. I wonder if the memory is now PMD aligned and marked as a 2M page? In iommu_page_make_shared() there is an explicit check for the level of the page being made shared being greater than PG_LEVEL_4K. If it is greater than 4K it does a psmash() and then continues. However, this check is only done if the PFN is not on a 2M boundary. That could result in RMPUPDATE returning FAIL_OVERLAP if the RMP has the range marked as 2M but the request is for a 4K page. What happens if you always take the if path iommu_page_make_shared()? @Usama, could you try making that modification and see if that helps? Thanks, Tom > >> >> Could this be a firmware bug? We are currently running 1.53 (below >> shows up in the dmesg). >> >> [ 22.245942] ccp 0000:41:00.1: SEV-SNP API:1.53 build:5 >> [ 22.308933] ccp 0000:41:00.1: SEV API:1.53 build:5 > > We are on > > [ 24.783307] ccp 0000:46:00.1: SEV-SNP API:1.55 build:29 > [ 24.844646] ccp 0000:46:00.1: SEV API:1.55 build:29 > > Is it possible to upgrade BIOS and verify? > > > Can you please share the dmesg of the booted system (before doing the kexec)? > > -Vasant > >