powerpc/kexec: Speedup kexec hash PTE tear down

Currently for kexec the PTE tear down on 1TB segment systems normally
requires 3 hcalls for each PTE removal. On a machine with 32GB of
memory it can take around a minute to remove all the PTEs.

This optimises the path so that we only remove PTEs that are valid.
It also uses the read 4 PTEs at once HCALL.  For the common case where
a PTEs is invalid in a 1TB segment, this turns the 3 HCALLs per PTE
down to 1 HCALL per 4 PTEs.

This gives an > 10x speedup in kexec times on PHYP, taking a 32GB
machine from around 1 minute down to a few seconds.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 20 insertions, 13 deletions

diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index 0707653612ba..cf79b46d8f88 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -367,21 +367,28 @@ static void pSeries_lpar_hptab_clear(void)
 {
         unsigned long size_bytes = 1UL << ppc64_pft_size;
         unsigned long hpte_count = size_bytes >> 4;
-        unsigned long dummy1, dummy2, dword0;
+        struct {
+                unsigned long pteh;
+                unsigned long ptel;
+        } ptes[4];
         long lpar_rc;
-        int i;
+        int i, j;
 
-        /* TODO: Use bulk call */
-        for (i = 0; i < hpte_count; i++) {
-                /* dont remove HPTEs with VRMA mappings */
-                lpar_rc = plpar_pte_remove_raw(H_ANDCOND, i, HPTE_V_1TB_SEG,
-                                                &dummy1, &dummy2);
-                if (lpar_rc == H_NOT_FOUND) {
-                        lpar_rc = plpar_pte_read_raw(0, i, &dword0, &dummy1);
-                        if (!lpar_rc && ((dword0 & HPTE_V_VRMA_MASK)
-                                != HPTE_V_VRMA_MASK))
-                                /* Can be hpte for 1TB Seg. So remove it */
-                                plpar_pte_remove_raw(0, i, 0, &dummy1, &dummy2);
+        /* Read in batches of 4,
+         * invalidate only valid entries not in the VRMA
+         * hpte_count will be a multiple of 4
+         */
+        for (i = 0; i < hpte_count; i += 4) {
+                lpar_rc = plpar_pte_read_4_raw(0, i, (void *)ptes);
+                if (lpar_rc != H_SUCCESS)
+                        continue;
+                for (j = 0; j < 4; j++){
+                        if ((ptes[j].pteh & HPTE_V_VRMA_MASK) ==
+                                HPTE_V_VRMA_MASK)
+                                continue;
+                        if (ptes[j].pteh & HPTE_V_VALID)
+                                plpar_pte_remove_raw(0, i + j, 0,
+                                        &(ptes[j].pteh), &(ptes[j].ptel));
                 }
         }
 }