xem.github.io | My Blog , Portfolio and CV | Portfolio library

The Intel's manual 3A, Section 11.5.3, provides an algorithm to globally disable the caches:

11.5.3 Preventing Caching

To disable the L1, L2, and L3 caches after they have been enabled and have received cache fills, perform the following steps:

1. Enter the no-fill cache mode. (Set the CD flag in control register CR0 to 1 and the NW flag to 0.
2. Flush all caches using the WBINVD instruction.
3. Disable the MTRRs and set the default memory type to uncached or set all MTRRs for the uncached memory type (see the discussion of the discussion of the TYPE field and the E flag in Section 11.11.2.1, “IA32_MTRR_DEF_TYPE MSR”).

The caches must be flushed (step 2) after the CD flag is set to ensure system memory coherency. If the caches are not flushed, cache hits on reads will still occur and data will be read from valid cache lines.

The intent of the three separate steps listed above addresses three distinct requirements: (i) discontinue new data replacing existing data in the cache (ii) ensure data already in the cache are evicted to memory, (iii) ensure subsequent memory references observe UC memory type semantics. Different processor implementation of caching control hardware may allow some variation of software implementation of these three requirements. See note below.

NOTES Setting the CD flag in control register CR0 modifies the processor’s caching behaviour as indicated in Table 11-5, but setting the CD flag alone may not be sufficient across all processor families to force the effective memory type for all physical memory to be UC nor does it force strict memory ordering, due to hardware implementation variations across different processor families. To force the UC memory type and strict memory ordering on all of physical memory, it is sufficient to either program the MTRRs for all physical memory to be UC memory type or disable all MTRRs.

For the Pentium 4 and Intel Xeon processors, after the sequence of steps given above has been executed, the cache lines containing the code between the end of the WBINVD instruction and before the MTRRS have actually been disabled may be retained in the cache hierarchy. Here, to remove code from the cache completely, a second WBINVD instruction must be executed after the MTRRs have been disabled.

That's a long quote but it boils down to this code