On Wed, Feb 01, 2023, Sean Christopherson wrote: > On Tue, Jan 31, 2023, Borislav Petkov wrote: > > Hey Sean, > > > > On Fri, Jan 20, 2023 at 02:10:46PM +1100, Alexey Kardashevskiy wrote: > > > Prior to SEV-ES, KVM stored/loaded host debug registers upon switching > > > to/from a VM. Changing those registers inside a running SEV VM > > > triggered #VC exit to KVM. > > > > > > SEV-ES added the encrypted state (ES) which uses an encrypted guest page > > > for the VM state (VMSA). The hardware saves/restores certain registers on > > > VMRUN/VMEXIT according to a swap type (A, B, C), see > > > "Table B-3. Swap Types" in the AMD Architecture Programmer’s Manual > > > volume 2. > > > > > > AMD Milan (Fam 19h) introduces support for the debug registers swapping. > > > DR6 and DR7 are always swapped. DR[0-3] and DR[0-3]_ADDR_MASK are swapped > > > a type B when SEV_FEATURES[5] ("DebugSwap") is set. > > > > > > Enable DebugSwap in VMSA. But only do so if CPUID Fn80000021_EAX[0] > > > ("NoNestedDataBp", "Processor ignores nested data breakpoints") is > > > supported by the SOC as otherwise a malicious SEV-ES guest can set up > > > data breakpoints on the #VC IDT entry/stack and cause an infinite loop. > > > > > > Eliminate DR7 and #DB intercepts as: > > > - they are not needed when DebugSwap is supported; > > > - #VC for these intercepts is most likely not supported anyway and > > > kills the VM. > > > Keep DR7 intercepted unless DebugSwap enabled to prevent the infinite #DB > > > loop DoS. > > > > ... > > > > ok to take this through the tip tree? > > I would prefer to take this through KVM, there's enough subtle complexity in this > code that it'd be nice to have it close by. > > If you're happy with patch 1, maybe ack that one and take it through KVM, and > route patch 3 through tip? Ah, you've already applied 1. That works too. I don't think KVM support for DebugSwap is going to make v6.3 no matter who takes what, so just base on the next version of this patch on tip/x86/cpu and I'll make a mental note to not try to grab this until after v6.3-rc1.