RISC-V: Fix IPI/RFENCE hmask on non-monotonic hartid ordering

If the boot CPU does not have the lowest hartid, "hartid - hbase" can
become negative, leading to an incorrect hmask, causing userspace to
crash with SEGV.  This is observed on e.g. Starlight Beta, where cpuid 1
maps to hartid 0, and cpuid 0 maps to hartid 1.

Fix this by detecting this case, and shifting the accumulated mask and
updating hbase, if possible.

Fixes: 26fb751ca37846c9 ("RISC-V: Do not use cpumask data structure for hartid bitmap")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Tested-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
index 22444cf..775d332 100644 (file)
--- a/arch/riscv/kernel/sbi.c
+++ b/arch/riscv/kernel/sbi.c
@@ -250,7 +250,7 @@ static void __sbi_set_timer_v02(uint64_t stime_value)
 
 static int __sbi_send_ipi_v02(const struct cpumask *cpu_mask)
 {
-       unsigned long hartid, cpuid, hmask = 0, hbase = 0;
+       unsigned long hartid, cpuid, hmask = 0, hbase = 0, htop = 0;
        struct sbiret ret = {0};
        int result;
 
@@ -259,16 +259,27 @@ static int __sbi_send_ipi_v02(const struct cpumask *cpu_mask)
 
        for_each_cpu(cpuid, cpu_mask) {
                hartid = cpuid_to_hartid_map(cpuid);
-               if (hmask && ((hbase + BITS_PER_LONG) <= hartid)) {
-                       ret = sbi_ecall(SBI_EXT_IPI, SBI_EXT_IPI_SEND_IPI,
-                                       hmask, hbase, 0, 0, 0, 0);
-                       if (ret.error)
-                               goto ecall_failed;
-                       hmask = 0;
-                       hbase = 0;
+               if (hmask) {
+                       if (hartid + BITS_PER_LONG <= htop ||
+                           hbase + BITS_PER_LONG <= hartid) {
+                               ret = sbi_ecall(SBI_EXT_IPI,
+                                               SBI_EXT_IPI_SEND_IPI, hmask,
+                                               hbase, 0, 0, 0, 0);
+                               if (ret.error)
+                                       goto ecall_failed;
+                               hmask = 0;
+                       } else if (hartid < hbase) {
+                               /* shift the mask to fit lower hartid */
+                               hmask <<= hbase - hartid;
+                               hbase = hartid;
+                       }
                }
-               if (!hmask)
+               if (!hmask) {
                        hbase = hartid;
+                       htop = hartid;
+               } else if (hartid > htop) {
+                       htop = hartid;
+               }
                hmask |= BIT(hartid - hbase);
        }
 
@@ -345,7 +356,7 @@ static int __sbi_rfence_v02(int fid, const struct cpumask *cpu_mask,
                            unsigned long start, unsigned long size,
                            unsigned long arg4, unsigned long arg5)
 {
-       unsigned long hartid, cpuid, hmask = 0, hbase = 0;
+       unsigned long hartid, cpuid, hmask = 0, hbase = 0, htop = 0;
        int result;
 
        if (!cpu_mask || cpumask_empty(cpu_mask))
@@ -353,16 +364,26 @@ static int __sbi_rfence_v02(int fid, const struct cpumask *cpu_mask,
 
        for_each_cpu(cpuid, cpu_mask) {
                hartid = cpuid_to_hartid_map(cpuid);
-               if (hmask && ((hbase + BITS_PER_LONG) <= hartid)) {
-                       result = __sbi_rfence_v02_call(fid, hmask, hbase,
-                                                      start, size, arg4, arg5);
-                       if (result)
-                               return result;
-                       hmask = 0;
-                       hbase = 0;
+               if (hmask) {
+                       if (hartid + BITS_PER_LONG <= htop ||
+                           hbase + BITS_PER_LONG <= hartid) {
+                               result = __sbi_rfence_v02_call(fid, hmask,
+                                               hbase, start, size, arg4, arg5);
+                               if (result)
+                                       return result;
+                               hmask = 0;
+                       } else if (hartid < hbase) {
+                               /* shift the mask to fit lower hartid */
+                               hmask <<= hbase - hartid;
+                               hbase = hartid;
+                       }
                }
-               if (!hmask)
+               if (!hmask) {
                        hbase = hartid;
+                       htop = hartid;
+               } else if (hartid > htop) {
+                       htop = hartid;
+               }
                hmask |= BIT(hartid - hbase);
        }