On Mon, Apr 6, 2026 at 5:07 PM Sean Christopherson <[email protected]> wrote: > > On Fri, Mar 27, 2026, Jim Mattson wrote: > > When KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT is disabled, verify that KVM > > correctly virtualizes the host PAT MSR and the guest PAT register for > > nested SVM guests. > > > > With nested NPT disabled: > > * L1 and L2 share the same PAT > > * The vmcb12.g_pat is ignored > > > > With nested NPT enabled: > > * An invalid g_pat in vmcb12 causes VMEXIT_INVALID > > * RDMSR(IA32_PAT) from L2 returns the value of the guest PAT register > > * WRMSR(IA32_PAT) from L2 is reflected in vmcb12's g_pat on VMEXIT > > * RDMSR(IA32_PAT) from L1 returns the value of the host PAT MSR > > * Save/restore with the vCPU in guest mode preserves both hPAT and gPAT > > > > Signed-off-by: Jim Mattson <[email protected]> > > --- > > tools/arch/x86/include/uapi/asm/kvm.h | 2 + > > Don't update uAPI headers in tools/, they're not used by KVM selftests (perf > folks will sync them as needed). > > > +#define PAT_DEFAULT 0x0007040600070406ULL > > +#define L1_PAT_VALUE 0x0007040600070404ULL /* Change PA0 to WT */ > > +#define L2_VMCB12_PAT 0x0606060606060606ULL /* All WB */ > > +#define L2_PAT_MODIFIED 0x0606060606060604ULL /* Change PA0 > > to WT */ > > +#define INVALID_PAT_VALUE 0x0808080808080808ULL /* 8 is reserved */ > > + > > +/* > > + * Shared state between L1 and L2 for verification. > > + */ > > +struct pat_test_data { > > + uint64_t l2_pat_read; > > + uint64_t l2_pat_after_write; > > + uint64_t l1_pat_after_vmexit; > > + uint64_t vmcb12_gpat_after_exit; > > + bool l2_done; > > +}; > > + > > +static struct pat_test_data *pat_data; > > This is ridiculous. Whatever AI you're using is reinventing > sync_global_to_guest() > in a very obfuscated way. Drop the indirection along with the params and the > full page allocation, and just sync the damn struct. > > Actually, this is even dumber than that. The "data" is only ever accessed > from > within the guest; it's used to pass info between L1 and L2. Drop the struct > entirely and just write global variables. > > In general, please clean this test up before submitting v8. All of the L2 > code > is basically copy+paste of itself. This is the second vibe coded selftest > (AFAIK) > you've posted, and it has many of the same flaws as the first one[*]. While > I'm > not opposed to using fancy tools, and the bar is generally lower for > selftests, > the code still needs to be readable and maintainable. This ain't. > > [*] https://lore.kernel.org/all/[email protected]
I contend that the kvm selftests infrastructure already fails to meet that bar, but I will toss this in the bit bucket and write a selftest by hand for the next version.
