diff mbox series

[v3] x86/hyperv: Replace kmap() with kmap_local_page()

Message ID 20221017093726.2070674-11-zhao1.liu@linux.intel.com
State New
Headers
Series [v3] x86/hyperv: Replace kmap() with kmap_local_page() |

Commit Message

Zhao Liu Oct. 17, 2022, 9:37 a.m. UTC 
  From: Zhao Liu <zhao1.liu@intel.com>

kmap() is being deprecated in favor of kmap_local_page()[1].

There are two main problems with kmap(): (1) It comes with an overhead as mapping space is restricted and protected by a global lock for synchronization and (2) it also requires global TLB invalidation when the kmap's pool wraps and it might block when the mapping space is fully utilized until a slot becomes available.

With kmap_local_page() the mappings are per thread, CPU local, can take page faults, and can be called from any context (including interrupts).
It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore, the tasks can be preempted and, when they are scheduled to run again, the kernel virtual addresses are restored and are still valid.

Since its use in hyperv/hv_init.c is safe, it should be preferred.

Therefore, replace kmap() with kmap_local_page() in hyperv/hv_init.c.

[1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com

Suggested-by: Ira Weiny <ira.weiny@intel.com>
Suggested-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>

---
Suggested by credits.
        Ira: Referred to his task documentation and review comments.
        Fabio: Stole some of his boiler plate commit message.

---
Changelog:
v2:
- Fix wrong incoming parameters in kunmap_local();
- Add Fabio as suggester since I quoted his commit message.

---
 arch/x86/hyperv/hv_init.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--
2.34.1

Comments

Zhao Liu Oct. 17, 2022, 9:53 a.m. UTC | #1 
Sorry, please ignore the last hyperv patch, I made a mistake.

Zhao

On Mon, Oct 17, 2022 at 05:37:26PM +0800, Zhao Liu wrote:
> Date: Mon, 17 Oct 2022 17:37:26 +0800
> From: Zhao Liu <zhao1.liu@linux.intel.com>
> Subject: [PATCH v3] x86/hyperv: Replace kmap() with kmap_local_page()
> X-Mailer: git-send-email 2.34.1
> 
> From: Zhao Liu <zhao1.liu@intel.com>
> 
> kmap() is being deprecated in favor of kmap_local_page()[1].
> 
> There are two main problems with kmap(): (1) It comes with an overhead as mapping space is restricted and protected by a global lock for synchronization and (2) it also requires global TLB invalidation when the kmap's pool wraps and it might block when the mapping space is fully utilized until a slot becomes available.
> 
> With kmap_local_page() the mappings are per thread, CPU local, can take page faults, and can be called from any context (including interrupts).
> It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore, the tasks can be preempted and, when they are scheduled to run again, the kernel virtual addresses are restored and are still valid.
> 
> Since its use in hyperv/hv_init.c is safe, it should be preferred.
> 
> Therefore, replace kmap() with kmap_local_page() in hyperv/hv_init.c.
> 
> [1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com
> 
> Suggested-by: Ira Weiny <ira.weiny@intel.com>
> Suggested-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> 
> ---
> Suggested by credits.
>         Ira: Referred to his task documentation and review comments.
>         Fabio: Stole some of his boiler plate commit message.
> 
> ---
> Changelog:
> v2:
> - Fix wrong incoming parameters in kunmap_local();
> - Add Fabio as suggester since I quoted his commit message.
> 
> ---
>  arch/x86/hyperv/hv_init.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index 3de6d8b53367..72fe46eb183f 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -459,13 +459,13 @@ void __init hyperv_init(void)
>                 wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
> 
>                 pg = vmalloc_to_page(hv_hypercall_pg);
> -               dst = kmap(pg);
> +               dst = kmap_local_page(pg);
>                 src = memremap(hypercall_msr.guest_physical_address << PAGE_SHIFT, PAGE_SIZE,
>                                 MEMREMAP_WB);
>                 BUG_ON(!(src && dst));
>                 memcpy(dst, src, HV_HYP_PAGE_SIZE);
>                 memunmap(src);
> -               kunmap(pg);
> +               kunmap_local(dst);
>         } else {
>                 hypercall_msr.guest_physical_address = vmalloc_to_pfn(hv_hypercall_pg);
>                 wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
> --
> 2.34.1
>
diff mbox series

Patch

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 3de6d8b53367..72fe46eb183f 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -459,13 +459,13 @@  void __init hyperv_init(void)
                wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);

                pg = vmalloc_to_page(hv_hypercall_pg);
-               dst = kmap(pg);
+               dst = kmap_local_page(pg);
                src = memremap(hypercall_msr.guest_physical_address << PAGE_SHIFT, PAGE_SIZE,
                                MEMREMAP_WB);
                BUG_ON(!(src && dst));
                memcpy(dst, src, HV_HYP_PAGE_SIZE);
                memunmap(src);
-               kunmap(pg);
+               kunmap_local(dst);
        } else {
                hypercall_msr.guest_physical_address = vmalloc_to_pfn(hv_hypercall_pg);
                wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);