On Tue, 2023-10-17 at 20:49 +0200, Borislav Petkov wrote: > On Tue, Oct 17, 2023 at 01:12:30PM -0500, John Allen wrote: > > I looked into using __rdmsr in an earlier revision of the patch, but > > found that it causes a build warning: > > > > ld: warning: orphan section `__ex_table' from `arch/x86/boot/compressed/sev.o' being placed in section `__ex_table' > > > > This is due to the __ex_table section not being used during > > decompression boot. Do you know of a way around this? > > Yeah, arch/x86/boot/msr.h. > > We did those a while ago. I guess they could be moved to > asm/shared/msr.h and renamed to something that is not a > "boot_" prefix. > > Something like > > rdmsr_without_any_exception_handling_and_other_gunk_don_t_you_even_think_of_adding() > > ... > > But srsly: > > raw_rdmsr() > raw_wrmsr() > > should be good, as tglx suggests offlist. > > You can do that in one patch and prepend your set with it. > > Thx. > Assuming that we will actually allow the guest to read the IA32_XSS, then it is correct, but otherwise we will need to return some cached value of IA32_XSS, the same as the guest wrote last time. Or another option: KVM can cache the last value that the guest wrote to IA32_XSS (I assume that the guest can write msrs by sharing the address and value via GHCB), and then use it when it constructs the CPUID. Best regards, Maxim Levitsky
