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Date: Fri, 17 Mar 2023 16:59:37 +0100
From: Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
To: linux-kernel@...r.kernel.org
Cc: netdev@...r.kernel.org, Richard Cochran <richardcochran@...il.com>,
Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 RESEND] ptp: kvm: Use decrypted memory in confidential
guest on x86
On 08/03/2023 16:05, Jeremi Piotrowski wrote:
> KVM_HC_CLOCK_PAIRING currently fails inside SEV-SNP guests because the
> guest passes an address to static data to the host. In confidential
> computing the host can't access arbitrary guest memory so handling the
> hypercall runs into an "rmpfault". To make the hypercall work, the guest
> needs to explicitly mark the memory as decrypted. Do that in
> kvm_arch_ptp_init(), but retain the previous behavior for
> non-confidential guests to save us from having to allocate memory.
>
> Add a new arch-specific function (kvm_arch_ptp_exit()) to free the
> allocation and mark the memory as encrypted again.
>
> Signed-off-by: Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
> ---
> Hi,
>
> I would love to not allocate a whole page just for this driver, swiotlb is
> decrypted but I don't have access to a 'struct device' here. Does anyone have
> any suggestion?
>
> Jeremi
>
Hi,
Does anyone have any comments or suggestions? Or can this be merged.
Jeremi
> Changes since v1:
> - forgot to commit include/linux/ptp_kvm.h
>
> drivers/ptp/ptp_kvm_arm.c | 4 +++
> drivers/ptp/ptp_kvm_common.c | 1 +
> drivers/ptp/ptp_kvm_x86.c | 59 +++++++++++++++++++++++++++++-------
> include/linux/ptp_kvm.h | 1 +
> 4 files changed, 54 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/ptp/ptp_kvm_arm.c b/drivers/ptp/ptp_kvm_arm.c
> index b7d28c8dfb84..e68e6943167b 100644
> --- a/drivers/ptp/ptp_kvm_arm.c
> +++ b/drivers/ptp/ptp_kvm_arm.c
> @@ -22,6 +22,10 @@ int kvm_arch_ptp_init(void)
> return 0;
> }
>
> +void kvm_arch_ptp_exit(void)
> +{
> +}
> +
> int kvm_arch_ptp_get_clock(struct timespec64 *ts)
> {
> return kvm_arch_ptp_get_crosststamp(NULL, ts, NULL);
> diff --git a/drivers/ptp/ptp_kvm_common.c b/drivers/ptp/ptp_kvm_common.c
> index 9141162c4237..2418977989be 100644
> --- a/drivers/ptp/ptp_kvm_common.c
> +++ b/drivers/ptp/ptp_kvm_common.c
> @@ -130,6 +130,7 @@ static struct kvm_ptp_clock kvm_ptp_clock;
> static void __exit ptp_kvm_exit(void)
> {
> ptp_clock_unregister(kvm_ptp_clock.ptp_clock);
> + kvm_arch_ptp_exit();
> }
>
> static int __init ptp_kvm_init(void)
> diff --git a/drivers/ptp/ptp_kvm_x86.c b/drivers/ptp/ptp_kvm_x86.c
> index 4991054a2135..902844cc1a17 100644
> --- a/drivers/ptp/ptp_kvm_x86.c
> +++ b/drivers/ptp/ptp_kvm_x86.c
> @@ -14,27 +14,64 @@
> #include <uapi/linux/kvm_para.h>
> #include <linux/ptp_clock_kernel.h>
> #include <linux/ptp_kvm.h>
> +#include <linux/set_memory.h>
>
> static phys_addr_t clock_pair_gpa;
> -static struct kvm_clock_pairing clock_pair;
> +static struct kvm_clock_pairing clock_pair_glbl;
> +static struct kvm_clock_pairing *clock_pair;
>
> int kvm_arch_ptp_init(void)
> {
> + struct page *p;
> long ret;
>
> if (!kvm_para_available())
> return -ENODEV;
>
> - clock_pair_gpa = slow_virt_to_phys(&clock_pair);
> - if (!pvclock_get_pvti_cpu0_va())
> - return -ENODEV;
> + if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
> + p = alloc_page(GFP_KERNEL | __GFP_ZERO);
> + if (!p)
> + return -ENOMEM;
> +
> + clock_pair = page_address(p);
> + ret = set_memory_decrypted((unsigned long)clock_pair, 1);
> + if (ret) {
> + __free_page(p);
> + clock_pair = NULL;
> + goto nofree;
> + }
> + } else {
> + clock_pair = &clock_pair_glbl;
> + }
> +
> + clock_pair_gpa = slow_virt_to_phys(clock_pair);
> + if (!pvclock_get_pvti_cpu0_va()) {
> + ret = -ENODEV;
> + goto err;
> + }
>
> ret = kvm_hypercall2(KVM_HC_CLOCK_PAIRING, clock_pair_gpa,
> KVM_CLOCK_PAIRING_WALLCLOCK);
> - if (ret == -KVM_ENOSYS)
> - return -ENODEV;
> + if (ret == -KVM_ENOSYS) {
> + ret = -ENODEV;
> + goto err;
> + }
>
> return ret;
> +
> +err:
> + kvm_arch_ptp_exit();
> +nofree:
> + return ret;
> +}
> +
> +void kvm_arch_ptp_exit(void)
> +{
> + if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
> + WARN_ON(set_memory_encrypted((unsigned long)clock_pair, 1));
> + free_page((unsigned long)clock_pair);
> + clock_pair = NULL;
> + }
> }
>
> int kvm_arch_ptp_get_clock(struct timespec64 *ts)
> @@ -49,8 +86,8 @@ int kvm_arch_ptp_get_clock(struct timespec64 *ts)
> return -EOPNOTSUPP;
> }
>
> - ts->tv_sec = clock_pair.sec;
> - ts->tv_nsec = clock_pair.nsec;
> + ts->tv_sec = clock_pair->sec;
> + ts->tv_nsec = clock_pair->nsec;
>
> return 0;
> }
> @@ -81,9 +118,9 @@ int kvm_arch_ptp_get_crosststamp(u64 *cycle, struct timespec64 *tspec,
> pr_err_ratelimited("clock pairing hypercall ret %lu\n", ret);
> return -EOPNOTSUPP;
> }
> - tspec->tv_sec = clock_pair.sec;
> - tspec->tv_nsec = clock_pair.nsec;
> - *cycle = __pvclock_read_cycles(src, clock_pair.tsc);
> + tspec->tv_sec = clock_pair->sec;
> + tspec->tv_nsec = clock_pair->nsec;
> + *cycle = __pvclock_read_cycles(src, clock_pair->tsc);
> } while (pvclock_read_retry(src, version));
>
> *cs = &kvm_clock;
> diff --git a/include/linux/ptp_kvm.h b/include/linux/ptp_kvm.h
> index c2e28deef33a..746fd67c3480 100644
> --- a/include/linux/ptp_kvm.h
> +++ b/include/linux/ptp_kvm.h
> @@ -14,6 +14,7 @@ struct timespec64;
> struct clocksource;
>
> int kvm_arch_ptp_init(void);
> +void kvm_arch_ptp_exit(void);
> int kvm_arch_ptp_get_clock(struct timespec64 *ts);
> int kvm_arch_ptp_get_crosststamp(u64 *cycle,
> struct timespec64 *tspec, struct clocksource **cs);
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