[PATCH v7 3/6] x86/sev: Allow for use of the early boot GHCB for PSC requests

Tom Lendacky
2023-04-04T17:26:42Z

Using a GHCB for a page stage change (as opposed to the MSR protocol)
allows for multiple pages to be processed in a single request. In prep
for early PSC requests in support of unaccepted memory, update the
invocation of vmgexit_psc() to be able to use the early boot GHCB and not
just the per-CPU GHCB structure.

In order to use the proper GHCB (early boot vs per-CPU), set a flag that
indicates when the per-CPU GHCBs are available and registered. For APs,
the per-CPU GHCBs are created before they are started and registered upon
startup, so this flag can be used globally for the BSP and APs instead of
creating a per-CPU flag. This will allow for a significant reduction in
the number of MSR protocol page state change requests when accepting
memory.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
arch/x86/kernel/sev.c | 61 +++++++++++++++++++++++++++----------------
1 file changed, 38 insertions(+), 23 deletions(-)

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index a3d76eb344d6..1717bc4558f7 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -117,7 +117,19 @@ static DEFINE_PER_CPU(struct sev_es_save_area *, sev_vmsa);

struct sev_config {
__u64 debug : 1,
- __reserved : 63;
+
+ /*
+ * A flag used by __set_pages_state() that indicates when the
+ * per-CPU GHCB has been created and registered and thus can be
+ * used by the BSP instead of the early boot GHCB.
+ *
+ * For APs, the per-CPU GHCB is created before they are started
+ * and registered upon startup, so this flag can be used globally
+ * for the BSP and APs.
+ */
+ ghcbs_initialized : 1,
+
+ __reserved : 62;
};

static struct sev_config sev_cfg __read_mostly;
@@ -660,7 +672,7 @@ static void pvalidate_pages(unsigned long vaddr, unsigned long npages, bool vali
}
}

-static void __init early_set_pages_state(unsigned long paddr, unsigned long npages, enum psc_op op)
+static void early_set_pages_state(unsigned long paddr, unsigned long npages, enum psc_op op)
{
unsigned long paddr_end;
u64 val;
@@ -754,26 +766,13 @@ void __init snp_prep_memory(unsigned long paddr, unsigned int sz, enum psc_op op
WARN(1, "invalid memory op %d\n", op);
}

-static int vmgexit_psc(struct snp_psc_desc *desc)
+static int vmgexit_psc(struct ghcb *ghcb, struct snp_psc_desc *desc)
{
int cur_entry, end_entry, ret = 0;
struct snp_psc_desc *data;
- struct ghcb_state state;
struct es_em_ctxt ctxt;
- unsigned long flags;
- struct ghcb *ghcb;

- /*
- * __sev_get_ghcb() needs to run with IRQs disabled because it is using
- * a per-CPU GHCB.
- */
- local_irq_save(flags);
-
- ghcb = __sev_get_ghcb(&state);
- if (!ghcb) {
- ret = 1;
- goto out_unlock;
- }
+ vc_ghcb_invalidate(ghcb);

/* Copy the input desc into GHCB shared buffer */
data = (struct snp_psc_desc *)ghcb->shared_buffer;
@@ -830,20 +829,18 @@ static int vmgexit_psc(struct snp_psc_desc *desc)
}

out:
- __sev_put_ghcb(&state);
-
-out_unlock:
- local_irq_restore(flags);
-
return ret;
}

static void __set_pages_state(struct snp_psc_desc *data, unsigned long vaddr,
unsigned long vaddr_end, int op)
{
+ struct ghcb_state state;
struct psc_hdr *hdr;
struct psc_entry *e;
+ unsigned long flags;
unsigned long pfn;
+ struct ghcb *ghcb;
int i;

hdr = &data->hdr;
@@ -873,8 +870,20 @@ static void __set_pages_state(struct snp_psc_desc *data, unsigned long vaddr,
i++;
}

- if (vmgexit_psc(data))
+ local_irq_save(flags);
+
+ if (sev_cfg.ghcbs_initialized)
+ ghcb = __sev_get_ghcb(&state);
+ else
+ ghcb = boot_ghcb;
+
+ if (!ghcb || vmgexit_psc(ghcb, data))
sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_PSC);
+
+ if (sev_cfg.ghcbs_initialized)
+ __sev_put_ghcb(&state);
+
+ local_irq_restore(flags);
}

static void set_pages_state(unsigned long vaddr, unsigned long npages, int op)
@@ -882,6 +891,10 @@ static void set_pages_state(unsigned long vaddr, unsigned long npages, int op)
unsigned long vaddr_end, next_vaddr;
struct snp_psc_desc desc;

+ /* Use the MSR protocol when a GHCB is not available. */
+ if (!boot_ghcb)
+ return early_set_pages_state(__pa(vaddr), npages, op);
+
vaddr = vaddr & PAGE_MASK;
vaddr_end = vaddr + (npages << PAGE_SHIFT);

@@ -1259,6 +1272,8 @@ void setup_ghcb(void)
if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
snp_register_per_cpu_ghcb();

+ sev_cfg.ghcbs_initialized = true;
+
return;
}

--
2.40.0