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Message-ID: <20221117181127.1859634-2-dionnaglaze@google.com>
Date: Thu, 17 Nov 2022 18:11:26 +0000
From: Dionna Glaze <dionnaglaze@...gle.com>
To: linux-kernel@...r.kernel.org, x86@...nel.org
Cc: Dionna Glaze <dionnaglaze@...gle.com>,
Thomas Lendacky <Thomas.Lendacky@....com>,
Paolo Bonzini <pbonzini@...hat.com>,
Joerg Roedel <jroedel@...e.de>, Ingo Molnar <mingo@...hat.com>,
Andy Lutomirsky <luto@...nel.org>,
John Allen <john.allen@....com>,
Herbert Xu <herbert@...dor.apana.org.au>,
"David S. Miller" <davem@...emloft.net>,
Peter Gonda <pgonda@...gle.com>
Subject: [PATCH v2 1/2] kvm: sev: Add SEV-SNP guest request throttling
The AMD-SP is a precious resource that doesn't have a scheduler other
than a mutex lock queue. To avoid customers from causing a DoS, we
implement a module_param-set rate limit with a default of 2 requests
per 2 seconds.
These defaults were chosen empirically with a the assumption that
current server-grade SEV-SNP machines will rarely exceed 128 VMs under
usual circumstance.
The 2 burst per 2 seconds means on average 1 request every second. We
allow 2 requests back to back to allow for the guest to query the
certificate length in an extended guest request without a pause. The
1 second average is our target for quality of service since empirical
tests show that 64 VMs can concurrently request an attestation report
with a maximum latency of 1 second. We don't anticipate more
concurrency than that for a seldom used request for a majority well-
behaved set of VMs. The majority point is decided as >64 VMs given
the assumed 128 VM count for "extreme load".
The throttling code is 2 << 32 given that invalid length is 1 and 2 is
the next available code. This was suggested by Tom Lendacky, and will
be included in a new revision of the GHCB specification.
Cc: Thomas Lendacky <Thomas.Lendacky@....com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Joerg Roedel <jroedel@...e.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Andy Lutomirsky <luto@...nel.org>
Cc: John Allen <john.allen@....com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Peter Gonda <pgonda@...gle.com>
Signed-off-by: Dionna Glaze <dionnaglaze@...gle.com>
---
arch/x86/include/asm/sev-common.h | 1 +
arch/x86/kvm/svm/sev.c | 29 +++++++++++++++++++++++++++++
arch/x86/kvm/svm/svm.h | 3 +++
3 files changed, 33 insertions(+)
diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index 9573ee1573ed..225b5e88f9a4 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -158,6 +158,7 @@ struct snp_psc_desc {
/* Guest message request error code */
#define SNP_GUEST_REQ_INVALID_LEN BIT_ULL(32)
+#define SNP_GUEST_REQ_THROTTLED (((u64)2) << 32)
#define GHCB_MSR_TERM_REQ 0x100
#define GHCB_MSR_TERM_REASON_SET_POS 12
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index a35cd9f33f16..3ced06c6e07a 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -61,6 +61,14 @@ module_param_named(sev_es, sev_es_enabled, bool, 0444);
/* enable/disable SEV-SNP support */
static bool sev_snp_enabled = true;
module_param_named(sev_snp, sev_snp_enabled, bool, 0444);
+
+/* Throttle guest requests to a burst # per this many seconds */
+unsigned int guest_request_throttle_s = 2;
+module_param(guest_request_throttle_s, int, 0444);
+
+/* Throttle guest requests to this many per the above many seconds */
+unsigned int guest_request_throttle_burst = 2;
+module_param(guest_request_throttle_burst, int, 0444);
#else
#define sev_enabled false
#define sev_es_enabled false
@@ -338,6 +346,9 @@ static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
init_srcu_struct(&sev->psc_srcu);
ret = sev_snp_init(&argp->error);
mutex_init(&sev->guest_req_lock);
+ ratelimit_state_init(&sev->snp_guest_msg_rs,
+ guest_request_throttle_s * HZ,
+ guest_request_throttle_burst);
} else {
ret = sev_platform_init(&argp->error);
}
@@ -3288,6 +3299,14 @@ static void snp_cleanup_guest_buf(struct sev_data_snp_guest_request *data, unsig
*rc = SEV_RET_INVALID_ADDRESS;
}
+static bool snp_throttle_guest_request(struct kvm_sev_info *sev) {
+ if (__ratelimit(&sev->snp_guest_msg_rs))
+ return false;
+
+ pr_info_ratelimited("svm: too many guest message requests\n");
+ return true;
+}
+
static void snp_handle_guest_request(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t resp_gpa)
{
struct sev_data_snp_guest_request data = {0};
@@ -3304,6 +3323,11 @@ static void snp_handle_guest_request(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t
sev = &to_kvm_svm(kvm)->sev_info;
+ if (snp_throttle_guest_request(sev)) {
+ rc = SNP_GUEST_REQ_THROTTLED;
+ goto e_fail;
+ }
+
mutex_lock(&sev->guest_req_lock);
rc = snp_setup_guest_buf(svm, &data, req_gpa, resp_gpa);
@@ -3341,6 +3365,11 @@ static void snp_handle_ext_guest_request(struct vcpu_svm *svm, gpa_t req_gpa, gp
sev = &to_kvm_svm(kvm)->sev_info;
+ if (snp_throttle_guest_request(sev)) {
+ rc = SNP_GUEST_REQ_THROTTLED;
+ goto e_fail;
+ }
+
data_gpa = vcpu->arch.regs[VCPU_REGS_RAX];
data_npages = vcpu->arch.regs[VCPU_REGS_RBX];
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index e68b3aab57d6..b2eaac449d60 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -18,6 +18,7 @@
#include <linux/kvm_types.h>
#include <linux/kvm_host.h>
#include <linux/bits.h>
+#include <linux/ratelimit.h>
#include <asm/svm.h>
#include <asm/sev-common.h>
@@ -95,6 +96,8 @@ struct kvm_sev_info {
void *snp_certs_data;
struct mutex guest_req_lock;
+ struct ratelimit_state snp_guest_msg_rs; /* Limit guest requests */
+
u64 sev_features; /* Features set at VMSA creation */
};
--
2.38.1.584.g0f3c55d4c2-goog
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