On 9/30/26 11:07 PM, Amit Machhiwal wrote:
get_d_signext() has two compounding bugs since its introduction in 2010: 1. The extraction mask 0x8FF silently drops bits 8-10 of the 12-bit D field (PPC ISA bits 21-23), corrupting any displacement that has any of those bits set. 2. The sign-magnitude idiom "-(d & 0x7ff)" is wrong for two's-complement: for D=0xFFC (encoding of -4) it returns -252 instead of -4. Together these errors produce a wrong effective address for psq_l, psq_lu, psq_st, and psq_stu whenever the displacement is negative or is a positive value >= 0x100 with bits 8-10 set — essentially any real-world paired- single stack-relative access. The D field occupies the bottom 12 bits of the instruction word (confirmed by the adjacent W and I extractions via inst_get_field(inst,16,16) and inst_get_field(inst,17,19)). Replace the open-coded logic with the standard sign_extend32(inst & 0xfff, 11), which correctly performs two's-complement sign extension from 12 bits to 32 bits. Fixes: 831317b605e7 ("KVM: PPC: Implement Paired Single emulation") Cc: [email protected] Signed-off-by: Amit Machhiwal <[email protected]> --- arch/powerpc/kvm/book3s_paired_singles.c | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-) diff --git a/arch/powerpc/kvm/book3s_paired_singles.c b/arch/powerpc/kvm/book3s_paired_singles.c index bc39c76c9d9f..532f96293de0 100644 --- a/arch/powerpc/kvm/book3s_paired_singles.c +++ b/arch/powerpc/kvm/book3s_paired_singles.c @@ -479,12 +479,7 @@ static bool kvmppc_inst_is_paired_single(struct kvm_vcpu *vcpu, u32 inst)static int get_d_signext(u32 inst){ - int d = inst & 0x8ff; - - if (d & 0x800) - return -(d & 0x7ff); - - return (d & 0x7ff); + return sign_extend32(inst & 0xfff, 11); }static int kvmppc_ps_three_in(struct kvm_vcpu *vcpu, bool rc,
If the intent was just to get the signed value based on bit11 (0 based index) then patch looks right. Reviewed-by: Shrikanth Hegde <[email protected]>
