Re: [RFC PATCH V2 01/18] x86/sev: Pvalidate memory gab for decompressing kernel

["Gupta, Pankaj" <pankaj.gupta@amd.com>]

Hi Tianyu,

Some minor nits below.

> Pvalidate needed pages for decompressing kernel. The E820_TYPE_RAM
> entry includes only validated memory. The kernel expects that the
> RAM entry's addr is fixed while the entry size is to be extended
> to cover addresses to the start of next entry. This patch increases
> the RAM entry size to cover all possilble memory addresses until

s/possilble/possible

> init_size.
> 
> Signed-off-by: Tianyu Lan <tiala@microsoft.com>
> ---
>   arch/x86/boot/compressed/head_64.S |  8 +++
>   arch/x86/boot/compressed/sev.c     | 84 ++++++++++++++++++++++++++++++
>   2 files changed, 92 insertions(+)
> 
> diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
> index d33f060900d2..818edaf5d0cf 100644
> --- a/arch/x86/boot/compressed/head_64.S
> +++ b/arch/x86/boot/compressed/head_64.S
> @@ -348,6 +348,14 @@ SYM_CODE_START(startup_64)
>   	cld
>   	cli
>   
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +	/* pvalidate memory on demand if SNP is enabled. */
> +	pushq	%rsi
> +	movq    %rsi, %rdi
> +	call 	pvalidate_for_startup_64
> +	popq	%rsi
> +#endif
> +
>   	/* Setup data segments. */
>   	xorl	%eax, %eax
>   	movl	%eax, %ds
> diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
> index 960968f8bf75..3a5a1ab16095 100644
> --- a/arch/x86/boot/compressed/sev.c
> +++ b/arch/x86/boot/compressed/sev.c
> @@ -12,8 +12,10 @@
>    */
>   #include "misc.h"
>   
> +#include <asm/msr-index.h>
>   #include <asm/pgtable_types.h>
>   #include <asm/sev.h>
> +#include <asm/svm.h>
>   #include <asm/trapnr.h>
>   #include <asm/trap_pf.h>
>   #include <asm/msr-index.h>
> @@ -21,6 +23,7 @@
>   #include <asm/ptrace.h>
>   #include <asm/svm.h>
>   #include <asm/cpuid.h>
> +#include <asm/e820/types.h>
>   
>   #include "error.h"
>   #include "../msr.h"
> @@ -117,6 +120,22 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt,
>   /* Include code for early handlers */
>   #include "../../kernel/sev-shared.c"
>   
> +/* Check SEV-SNP via MSR */
> +static bool sev_snp_runtime_check(void)
> +{
> +	unsigned long low, high;
> +	u64 val;
> +
> +	asm volatile("rdmsr\n" : "=a" (low), "=d" (high) :
> +			"c" (MSR_AMD64_SEV));
> +
> +	val = (high << 32) | low;
> +	if (val & MSR_AMD64_SEV_SNP_ENABLED)
> +		return true;
> +
> +	return false;
> +}
> +
>   static inline bool sev_snp_enabled(void)
>   {
>   	return sev_status & MSR_AMD64_SEV_SNP_ENABLED;
> @@ -456,3 +475,68 @@ void sev_prep_identity_maps(unsigned long top_level_pgt)
>   
>   	sev_verify_cbit(top_level_pgt);
>   }
> +
> +static void extend_e820_on_demand(struct boot_e820_entry *e820_entry,
> +				  u64 needed_ram_end)
> +{
> +	u64 end, paddr;
> +	unsigned long eflags;
> +	int rc;
> +
> +	if (!e820_entry)
> +		return;
> +
> +	/* Validated memory must be aligned by PAGE_SIZE. */
> +	end = ALIGN(e820_entry->addr + e820_entry->size, PAGE_SIZE);
> +	if (needed_ram_end > end && e820_entry->type == E820_TYPE_RAM) {

maybe "if check" can be used to return from here, would read code better?

> +		for (paddr = end; paddr < needed_ram_end; paddr += PAGE_SIZE) 
Maybe we could reuse 'pvalidate_pages' here?

> +			rc = pvalidate(paddr, RMP_PG_SIZE_4K, true);
> +			if (rc) {
> +				error("Failed to validate address.n");

Would it make sense to print the cause of failure here?

> +				return;
> +			}
> +		}
> +		e820_entry->size = needed_ram_end - e820_entry->addr;
> +	}
> +}
> +
> +/*
> + * Explicitly pvalidate needed pages for decompressing the kernel.
> + * The E820_TYPE_RAM entry includes only validated memory. The kernel
> + * expects that the RAM entry's addr is fixed while the entry size is to be
> + * extended to cover addresses to the start of next entry.
> + * The function increases the RAM entry size to cover all possible memory
> + * addresses until init_size.
> + * For example,  init_end = 0x4000000,
> + * [RAM: 0x0 - 0x0],                       M[RAM: 0x0 - 0xa0000]
> + * [RSVD: 0xa0000 - 0x10000]                [RSVD: 0xa0000 - 0x10000]
> + * [ACPI: 0x10000 - 0x20000]      ==>       [ACPI: 0x10000 - 0x20000]
> + * [RSVD: 0x800000 - 0x900000]              [RSVD: 0x800000 - 0x900000]
> + * [RAM: 0x1000000 - 0x2000000]            M[RAM: 0x1000000 - 0x2001000]
> + * [RAM: 0x2001000 - 0x2007000]            M[RAM: 0x2001000 - 0x4000000]
> + * Other RAM memory after init_end is pvalidated by ms_hyperv_init_platform
> + */
> +__visible void pvalidate_for_startup_64(struct boot_params *boot_params)
> +{
> +	struct boot_e820_entry *e820_entry;
> +	u64 init_end =
> +		boot_params->hdr.pref_address + boot_params->hdr.init_size;
> +	u8 i, nr_entries = boot_params->e820_entries;
> +	u64 needed_end;

Could not very well interpret the name 'needed_end'.

> +
> +	if (!sev_snp_runtime_check())
> +		return;
> +
> +	for (i = 0; i < nr_entries; ++i) {
> +		/* Pvalidate memory holes in e820 RAM entries. */

Pvalidate and pvalidate names are used interchangeably in comments.

> +		e820_entry = &boot_params->e820_table[i];
> +		if (i < nr_entries - 1) {
> +			needed_end = boot_params->e820_table[i + 1].addr;
> +			if (needed_end < e820_entry->addr)
> +				error("e820 table is not sorted.\n");
> +		} else {
> +			needed_end = init_end;
> +		}
> +		extend_e820_on_demand(e820_entry, needed_end);
> +	}
> +}