ArmPkg/ArmMmuLib AARCH64: get rid of needless TLB invalidation

Currently, we always invalidate the TLBs entirely after making
any modification to the page tables. Now that we have introduced
strict memory permissions in quite a number of places, such
modifications occur much more often, and it is better for performance
to flush only those TLB entries that are actually affected by
the changes.

At the same time, relax some system wide data synchronization barriers
to non-shared. When running in UEFI, we don't share virtual address
translations with other masters, unless we are running under virt, but
in that case, the host will upgrade them as appropriate (by setting
an override at EL2)

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>

ArmPkg/Library/ArmLib/AArch64/ArmLibSupport.S

@@ -124,15 +124,15 @@ ASM_FUNC(ArmSetMAIR)
 //  IN VOID  *MVA                    // X1
 //  );
 ASM_FUNC(ArmUpdateTranslationTableEntry)
-   dc      civac, x0             // Clean and invalidate data line
-   dsb     sy
+   dsb     nshst
+   lsr     x1, x1, #12
    EL1_OR_EL2_OR_EL3(x0)
 1: tlbi    vaae1, x1             // TLB Invalidate VA , EL1
    b       4f
 2: tlbi    vae2, x1              // TLB Invalidate VA , EL2
    b       4f
 3: tlbi    vae3, x1              // TLB Invalidate VA , EL3
-4: dsb     sy
+4: dsb     nsh
    isb
    ret