Re: [dpdk-dev] [PATCH] bus/pci: check if 5-level paging is enabled when testing IOMMU address width

[Burakov, Anatoly]

On 05-Aug-18 7:41 PM, Drocula wrote:
The kernel version 4.14 released with the support of 5-level paging.
When PML5 enabled, user-space virtual addresses uses up to 56 bits.
see kernel's Documentation/x86/x86_64/mm.txt.
Signed-off-by: Drocula <quze...@gmail.com>
---
  drivers/bus/pci/linux/pci.c | 27 +++++++++++++++++++++++++--
  1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/drivers/bus/pci/linux/pci.c b/drivers/bus/pci/linux/pci.c
index 004600f..8913d6d 100644
--- a/drivers/bus/pci/linux/pci.c
+++ b/drivers/bus/pci/linux/pci.c
@@ -4,6 +4,7 @@
  
  #include <string.h>
  #include <dirent.h>
+#include <sys/mman.h>
  
  #include <rte_log.h>
  #include <rte_bus.h>
@@ -553,12 +554,34 @@
  }
  
  #if defined(RTE_ARCH_X86)
+/*
+ * Try to detect whether the system uses 5-level page table.
+ */
+static bool
+system_uses_PML5(void)
+{
+       void *page_4k, *mask = (void *)0xf0000000000000;
+       page_4k = mmap(mask, 4096, PROT_READ | PROT_WRITE,
+               MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+
+       if (page_4k == (void *) -1)
+               return false;

Shouldn't this be MAP_FAILED?

+       munmap(page_4k, 4096);
+
+       if ((unsigned long)page_4k & (unsigned long)mask)
+               return true;
+       return false;
+}
+
  static bool
  pci_one_device_iommu_support_va(struct rte_pci_device *dev)
  {
  #define VTD_CAP_MGAW_SHIFT    16
  #define VTD_CAP_MGAW_MASK     (0x3fULL << VTD_CAP_MGAW_SHIFT)
-#define X86_VA_WIDTH 47 /* From Documentation/x86/x86_64/mm.txt */
+/*  From Documentation/x86/x86_64/mm.txt */
+#define X86_VA_WIDTH_PML4 47
+#define X86_VA_WIDTH_PML5 56
+
        struct rte_pci_addr *addr = &dev->addr;
        char filename[PATH_MAX];
        FILE *fp;
@@ -589,7 +612,7 @@
        fclose(fp);
  
  	mgaw = ((vtd_cap_reg & VTD_CAP_MGAW_MASK) >> VTD_CAP_MGAW_SHIFT) + 1;
-       if (mgaw < X86_VA_WIDTH)
+       if (mgaw < (system_uses_PML5() ? X86_VA_WIDTH_PML5 : X86_VA_WIDTH_PML4))

This is perhaps nitpicking and a question of personal preferences, but i 
think storing this in a var would be more readable than doing ternary 
operator inside of an if statement.

                return false;
  
  	return true;



--
Thanks,
Anatoly