Messages in this thread Patch in this message | | | From | Tom Lendacky <> | Subject | [PATCH v1 1/2] x86/sev: Use per-CPU PSC structure in prep for unaccepted memory support | Date | Fri, 29 Jul 2022 09:01:14 -0500 |
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In advance of providing support for unaccepted memory, switch from using kmalloc() for allocating the Page State Change structure to using a per-CPU structure. This is needed to avoid a possible recursive call into set_pages_state() if the allocation requires (more) memory to be accepted, which would result in a hang.
Protect the use of the per-CPU structure by disabling interrupts during memory acceptance. Since the set_pages_state() path is the only path into vmgexit_psc(), rename vmgexit_psc() to __vmgexit_psc() and remove the calls to disable interrupts which are now performed by set_pages_state().
Even with interrupts disabled, an NMI can be raised while performing memory acceptance. The NMI could then cause further memory acceptance to performed. To prevent corruption to the per-CPU structure, use the PSC MSR protocol in this situation.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com> --- arch/x86/kernel/sev.c | 60 ++++++++++++++++++++++++++++--------------- 1 file changed, 39 insertions(+), 21 deletions(-)
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c index c05f0124c410..1f7f6205c4f6 100644 --- a/arch/x86/kernel/sev.c +++ b/arch/x86/kernel/sev.c @@ -104,6 +104,15 @@ struct sev_es_runtime_data { * is currently unsupported in SEV-ES guests. */ unsigned long dr7; + + /* + * Page State Change structure for use when accepting memory or when + * changing page state. Interrupts are disabled when using the structure + * but an NMI could still be raised, so use a flag to indicate when the + * structure is in use and use the MSR protocol in these cases. + */ + struct snp_psc_desc psc_desc; + bool psc_active; }; struct ghcb_state { @@ -660,7 +669,7 @@ static void pvalidate_pages(unsigned long vaddr, unsigned int npages, bool valid } } -static void __init early_set_pages_state(unsigned long paddr, unsigned int npages, enum psc_op op) +static void early_set_pages_state(unsigned long paddr, unsigned int npages, enum psc_op op) { unsigned long paddr_end; u64 val; @@ -742,26 +751,17 @@ 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 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; - } + if (!ghcb) + return 1; /* Copy the input desc into GHCB shared buffer */ data = (struct snp_psc_desc *)ghcb->shared_buffer; @@ -820,9 +820,6 @@ static int vmgexit_psc(struct snp_psc_desc *desc) out: __sev_put_ghcb(&state); -out_unlock: - local_irq_restore(flags); - return ret; } @@ -861,18 +858,32 @@ static void __set_pages_state(struct snp_psc_desc *data, unsigned long vaddr, i++; } - if (vmgexit_psc(data)) + if (__vmgexit_psc(data)) sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_PSC); } static void set_pages_state(unsigned long vaddr, unsigned int npages, int op) { unsigned long vaddr_end, next_vaddr; + struct sev_es_runtime_data *data; struct snp_psc_desc *desc; + unsigned long flags; - desc = kmalloc(sizeof(*desc), GFP_KERNEL_ACCOUNT); - if (!desc) - panic("SNP: failed to allocate memory for PSC descriptor\n"); + /* Disable interrupts since a per-CPU PSC and per-CPU GHCB are used. */ + local_irq_save(flags); + + data = this_cpu_read(runtime_data); + if (!data || data->psc_active) { + /* No per-CPU PSC or it is active, use the MSR protocol. */ + early_set_pages_state(__pa(vaddr), npages, op); + goto out; + } + + /* Mark the PSC in use. */ + data->psc_active = true; + barrier(); + + desc = &data->psc_desc; vaddr = vaddr & PAGE_MASK; vaddr_end = vaddr + (npages << PAGE_SHIFT); @@ -887,7 +898,12 @@ static void set_pages_state(unsigned long vaddr, unsigned int npages, int op) vaddr = next_vaddr; } - kfree(desc); + /* Mark the PSC no longer in use. */ + barrier(); + data->psc_active = false; + +out: + local_irq_restore(flags); } void snp_set_memory_shared(unsigned long vaddr, unsigned int npages) @@ -1339,6 +1355,8 @@ static void __init alloc_runtime_data(int cpu) panic("Can't allocate SEV-ES runtime data"); per_cpu(runtime_data, cpu) = data; + + data->psc_active = false; } static void __init init_ghcb(int cpu) -- 2.36.1
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