mshv: Fix infinite fault loop on permission-denied GPA intercepts

mshv: Fix infinite fault loop on permission-denied GPA intercepts

Prevent infinite fault loops when guests access memory regions without
proper permissions. Currently, mshv_handle_gpa_intercept() attempts to
remap pages for all faults on movable memory regions, regardless of
whether the access type is permitted. When a guest writes to a read-only
region, the remap succeeds but the region remains read-only, causing
immediate re-fault and spinning the vCPU indefinitely.

Validate intercept access type against region permissions before
attempting remaps. Reject writes to non-writable regions and executes to
non-executable regions early, returning false to let the VMM handle the
intercept appropriately.

This also closes a potential DoS vector where malicious guests could
intentionally trigger these fault loops to consume host resources.

Fixes: b9a66cd5ccbb ("mshv: Add support for movable memory regions")
Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Reviewed-by: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>