[PATCH v8 5/7] x86/sev: Add interface to re-enable RMP optimizations.

[Ashish Kalra]

From: Ashish Kalra <ashish.kalra@xxxxxxx>

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.

The interface uses mod_delayed_work() instead of queue_delayed_work()
so that the delay timer is reset on each call. This provides proper
batching semantics: re-optimization runs 10 seconds after the *last*
VM termination rather than after the first. mod_delayed_work() also
re-queues work that is already in-flight, so a re-scan request
during an active scan is not silently dropped.

Reviewed-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
---
 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 0d662221615a..a11306f25336 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_clear_rmpopt_configured(void);
 void snp_shutdown(void);
@@ -682,6 +683,7 @@ 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_clear_rmpopt_configured(void) {}
 static inline void snp_shutdown(void) {}
diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index b63b639bfc30..253a534b9a0d 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -782,6 +782,21 @@ 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) || !rmpopt_configured)
+		return;
+
+	guard(mutex)(&rmpopt_wq_mutex);
+
+	if (!rmpopt_wq)
+		return;
+
+	mod_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