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SubjectRe: [PATCH] KVM: SVM: Replace kmap_atomic() with kmap_local_page()
On Fri, Sep 02, 2022, Zhao Liu wrote:
> From: Zhao Liu <zhao1.liu@intel.com>
>
> The use of kmap_atomic() is being deprecated in favor of
> kmap_local_page()[1].
>
> In arch/x86/kvm/svm/sev.c, the function sev_clflush_pages() doesn't
> need to disable pagefaults and preemption in kmap_atomic(). It can
> simply use kmap_local_page() / kunmap_local() that can instead do the
> mapping / unmapping regardless of the context.
>
> With kmap_local_page(), the mapping is per thread, CPU local and not
> globally visible. Therefore, sev_clflush_pages() is a function where
> the use of kmap_local_page() in place of kmap_atomic() is correctly
> suited.
>
> Convert the calls of kmap_atomic() / kunmap_atomic() to
> kmap_local_page() / kunmap_local().
>
> [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 document and review comments.
> Fabio: Referred to his boiler plate commit message.
> ---
> arch/x86/kvm/svm/sev.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 28064060413a..12747c7bda4e 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -465,9 +465,9 @@ static void sev_clflush_pages(struct page *pages[], unsigned long npages)
> return;
>
> for (i = 0; i < npages; i++) {
> - page_virtual = kmap_atomic(pages[i]);
> + page_virtual = kmap_local_page(pages[i]);
> clflush_cache_range(page_virtual, PAGE_SIZE);

SEV is 64-bit only, any reason not to go straight to page_address()?

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 28064060413a..aaf39e3c7bb5 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -457,7 +457,6 @@ static void sev_unpin_memory(struct kvm *kvm, struct page **pages,

static void sev_clflush_pages(struct page *pages[], unsigned long npages)
{
- uint8_t *page_virtual;
unsigned long i;

if (this_cpu_has(X86_FEATURE_SME_COHERENT) || npages == 0 ||
@@ -465,9 +464,7 @@ static void sev_clflush_pages(struct page *pages[], unsigned long npages)
return;

for (i = 0; i < npages; i++) {
- page_virtual = kmap_atomic(pages[i]);
- clflush_cache_range(page_virtual, PAGE_SIZE);
- kunmap_atomic(page_virtual);
+ clflush_cache_range(page_address(pages[i]), PAGE_SIZE);
cond_resched();
}
}

config KVM_AMD_SEV
def_bool y
bool "AMD Secure Encrypted Virtualization (SEV) support"
depends on KVM_AMD && X86_64 <==================================
> - kunmap_atomic(page_virtual);
> + kunmap_local(page_virtual);
> cond_resched();
> }
> }
> --
> 2.34.1
>

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