[PATCH Part2 v6 49/49] KVM: SVM: Sync the GHCB scratch buffer using already mapped ghcb

Ashish Kalra
2022-06-20T23:15:57Z

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

Using kvm_write_guest() to sync the GHCB scratch buffer can fail
due to host mapping being 2M, but RMP being 4K. The page fault handling
in do_user_addr_fault() fails to split the 2M page to handle RMP fault due
to it being called here in a non-preemptible context. Instead use
the already kernel mapped ghcb to sync the scratch buffer when the
scratch buffer is contained within the GHCB.

Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
---
arch/x86/kvm/svm/sev.c | 29 +++++++++++++++++++++--------
arch/x86/kvm/svm/svm.h | 2 ++
2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 2c88215a111f..e1dd67e12774 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2944,6 +2944,24 @@ static bool sev_es_sync_to_ghcb(struct vcpu_svm *svm)
ghcb_set_sw_exit_info_1(ghcb, svm->sev_es.ghcb_sw_exit_info_1);
ghcb_set_sw_exit_info_2(ghcb, svm->sev_es.ghcb_sw_exit_info_2);

+ /* Sync the scratch buffer area. */
+ if (svm->sev_es.ghcb_sa_sync) {
+ if (svm->sev_es.ghcb_sa_contained) {
+ memcpy(ghcb->shared_buffer + svm->sev_es.ghcb_sa_offset,
+ svm->sev_es.ghcb_sa, svm->sev_es.ghcb_sa_len);
+ } else {
+ int ret;
+
+ ret = kvm_write_guest(svm->vcpu.kvm,
+ svm->sev_es.ghcb_sa_gpa,
+ svm->sev_es.ghcb_sa, svm->sev_es.ghcb_sa_len);
+ if (ret)
+ pr_warn_ratelimited("unmap_ghcb: kvm_write_guest failed while syncing scratch area, gpa: %llx, ret: %d\n",
+ svm->sev_es.ghcb_sa_gpa, ret);
+ }
+ svm->sev_es.ghcb_sa_sync = false;
+ }
+
trace_kvm_vmgexit_exit(svm->vcpu.vcpu_id, ghcb);

svm_unmap_ghcb(svm, &map);
@@ -3156,14 +3174,6 @@ void sev_es_unmap_ghcb(struct vcpu_svm *svm)
if (!svm->sev_es.ghcb_in_use)
return;

- /* Sync the scratch buffer area. */
- if (svm->sev_es.ghcb_sa_sync) {
- kvm_write_guest(svm->vcpu.kvm,
- svm->sev_es.ghcb_sa_gpa,
- svm->sev_es.ghcb_sa, svm->sev_es.ghcb_sa_len);
- svm->sev_es.ghcb_sa_sync = false;
- }
-
sev_es_sync_to_ghcb(svm);

svm->sev_es.ghcb_in_use = false;
@@ -3229,6 +3239,8 @@ static int setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
scratch_gpa_beg, scratch_gpa_end);
goto e_scratch;
}
+ svm->sev_es.ghcb_sa_contained = true;
+ svm->sev_es.ghcb_sa_offset = scratch_gpa_beg - ghcb_scratch_beg;
} else {
/*
* The guest memory must be read into a kernel buffer, so
@@ -3239,6 +3251,7 @@ static int setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
len, GHCB_SCRATCH_AREA_LIMIT);
goto e_scratch;
}
+ svm->sev_es.ghcb_sa_contained = false;
}

if (svm->sev_es.ghcb_sa_alloc_len < len) {
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 7b14b5ef1f8c..2cdfc79bf2cf 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -210,6 +210,8 @@ struct vcpu_sev_es_state {
u64 ghcb_sa_gpa;
u32 ghcb_sa_alloc_len;
bool ghcb_sa_sync;
+ bool ghcb_sa_contained;
+ u32 ghcb_sa_offset;

/*
* SEV-ES support to hold the sw_exit_info return values to be
--
2.25.1