[PATCH v6 4/6] x86/sev: Add interface to re-enable RMP optimizations.

[Ashish Kalra <Ashish.Kalra@amd.com>]

From: Ashish Kalra <ashish.kalra@amd.com>

RMPOPT table is a per-CPU table which indicates if 1GB regions of
physical memory are entirely hypervisor-owned or not.

When performing host memory accesses in hypervisor mode as well as
non-SNP guest mode, the processor may consult the RMPOPT table to
potentially skip an RMP access and improve performance.

Events such as RMPUPDATE can clear RMP optimizations. Add an interface
to re-enable those optimizations.

Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
---
 arch/x86/include/asm/sev.h |  2 ++
 arch/x86/virt/svm/sev.c    | 15 +++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 6fd72a44a51e..09b1c5d33790 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -662,6 +662,7 @@ static inline void snp_leak_pages(u64 pfn, unsigned int pages)
 	__snp_leak_pages(pfn, pages, true);
 }
 int snp_prepare(void);
+void snp_rmpopt_all_physmem(void);
 void snp_setup_rmpopt(void);
 void snp_shutdown(void);
 #else
@@ -681,6 +682,7 @@ static inline void snp_leak_pages(u64 pfn, unsigned int npages) {}
 static inline void kdump_sev_callback(void) { }
 static inline void snp_fixup_e820_tables(void) {}
 static inline int snp_prepare(void) { return -ENODEV; }
+static inline void snp_rmpopt_all_physmem(void) {}
 static inline void snp_setup_rmpopt(void) {}
 static inline void snp_shutdown(void) {}
 #endif
diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index d7e40a5fe5ca..4442ecae3d18 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -741,6 +741,21 @@ static void rmpopt_work_handler(struct work_struct *work)
 	free_cpumask_var(follower_mask);
 }
 
+void snp_rmpopt_all_physmem(void)
+{
+	if (!cpu_feature_enabled(X86_FEATURE_RMPOPT))
+		return;
+
+	guard(mutex)(&rmpopt_wq_mutex);
+
+	if (!rmpopt_wq)
+		return;
+
+	queue_delayed_work(rmpopt_wq, &rmpopt_delayed_work,
+			   msecs_to_jiffies(RMPOPT_WORK_TIMEOUT));
+}
+EXPORT_SYMBOL_GPL(snp_rmpopt_all_physmem);
+
 void snp_setup_rmpopt(void)
 {
 	u64 rmpopt_base;
-- 
2.43.0