Messages in this thread | | | Date | Thu, 9 Jun 2022 15:55:55 +0800 | Subject | Re: [PATCH V2] x86/Hyper-V: Add SEV negotiate protocol support in Isolation VM | From | Tianyu Lan <> |
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Hi Michael: Thanks for your review.
On 6/8/2022 4:30 AM, Michael Kelley (LINUX) wrote: >> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c >> index 8b392b6b7b93..40b6874accdb 100644 >> --- a/arch/x86/hyperv/hv_init.c >> +++ b/arch/x86/hyperv/hv_init.c >> @@ -29,6 +29,7 @@ >> #include <clocksource/hyperv_timer.h> >> #include <linux/highmem.h> >> #include <linux/swiotlb.h> >> +#include <asm/sev.h> >> >> int hyperv_init_cpuhp; >> u64 hv_current_partition_id = ~0ull; >> @@ -70,6 +71,11 @@ static int hyperv_init_ghcb(void) >> ghcb_base = (void **)this_cpu_ptr(hv_ghcb_pg); >> *ghcb_base = ghcb_va; >> >> + /* Negotiate GHCB Version. */ >> + if (!hv_ghcb_negotiate_protocol()) >> + hv_ghcb_terminate(SEV_TERM_SET_GEN, >> + GHCB_SEV_ES_PROT_UNSUPPORTED); >> + > Negotiating the protocol here is unexpected for me. The > function hyperv_init_ghcb() is called for each CPU as it > initializes, so the static variable ghcb_version will be set > multiple times. I can see that setup_ghbc(), which this is > patterned after, is also called for each CPU during the early > CPU initialization, which is also a bit weird. I see two > problems: > > 1) hv_ghcb_negotiate_protocol() could get called in parallel > on two different CPUs at the same time, and the Hyper-V > version modifies global state (the MSR_AMD64_SEV_ES_GHCB > MSR). I'm not sure if the sev_es version has the same > problem. > > 2) The Hyper-V version would get called when taking a CPU > from on offline state to an online state. I'm not sure if taking > CPUs online and offline is allowed in an SNP isolated VM, but > if it is, then ghcb_version could be modified well after Linux > initialization, violating the __ro_after_init qualifier on the > variable. > > Net, it seems like we should find a way to negotiate the > GHCB version only once at boot time.
Yes, this makes sense and will update. > >> diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c >> index 2b994117581e..4b67c4d7c4f5 100644 >> --- a/arch/x86/hyperv/ivm.c >> +++ b/arch/x86/hyperv/ivm.c >> @@ -53,6 +53,8 @@ union hv_ghcb { >> } hypercall; >> } __packed __aligned(HV_HYP_PAGE_SIZE); >> >> +static u16 ghcb_version __ro_after_init; >> + > This is same name as the equivalent sev_es variable. Could this one > be changed to hv_ghcb_version to avoid any confusion? > >> +static inline void wr_ghcb_msr(u64 val) >> +{ >> + u32 low, high; >> + >> + low = (u32)(val); >> + high = (u32)(val >> 32); >> + >> + native_wrmsr(MSR_AMD64_SEV_ES_GHCB, low, high); > This whole function could be coded as just > > native_wrmsrl(MSR_AMD64_SEV_ES_GHCB, val); > > since the "l" version handles breaking the 64-bit argument > into two 32-bit arguments.
This follows SEV ES code and will update.
> >> +} >> + >> +static enum es_result ghcb_hv_call(struct ghcb *ghcb, u64 exit_code, >> + u64 exit_info_1, u64 exit_info_2) > Seems like the function name here should be hv_ghcb_hv_call. > >> @@ -152,8 +229,7 @@ void hv_ghcb_msr_read(u64 msr, u64 *value) >> } >> >> ghcb_set_rcx(&hv_ghcb->ghcb, msr); >> - if (sev_es_ghcb_hv_call(&hv_ghcb->ghcb, false, &ctxt, >> - SVM_EXIT_MSR, 0, 0)) >> + if (ghcb_hv_call(&hv_ghcb->ghcb, SVM_EXIT_MSR, 0, 0)) >> pr_warn("Fail to read msr via ghcb %llx.\n", msr); >> else >> *value = (u64)lower_32_bits(hv_ghcb->ghcb.save.rax) > Since these changes remove the two cases where sev_es_ghcb_hv_call() > is invoked with the 2nd argument as "false", it seems like there should be > a follow-on patch to remove that argument and Hyper-V specific hack > from sev_es_ghcb_hv_call().
OK. Will update.
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