Re: [Xen-devel] [PATCH v3 08/11] pvh/acpi: Handle ACPI accesses for PVH guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.11.16 at 22:00, <boris.ostrovsky@xxxxxxxxxx> wrote:
> --- a/xen/arch/x86/hvm/ioreq.c
> +++ b/xen/arch/x86/hvm/ioreq.c
> @@ -16,6 +16,7 @@
>   * this program; If not, see <http://www.gnu.org/licenses/>.
>   */
>  
> +#include <xen/acpi.h>
>  #include <xen/config.h>
>  #include <xen/ctype.h>
>  #include <xen/init.h>

Please take the opportunity and remove the pointless xen/config.h
inclusion at once.

> @@ -1383,7 +1384,91 @@ static int hvm_access_cf8(
>  static int acpi_ioaccess(
>      int dir, unsigned int port, unsigned int bytes, uint32_t *val)
>  {
> -    return X86EMUL_UNHANDLEABLE;
> +    uint8_t *reg = NULL;
> +    const uint8_t *mask = NULL;
> +    bool is_cpu_map = false;
> +    struct domain *currd = current->domain;

const?

> +    const static uint8_t pm1a_mask[4] = {ACPI_BITMASK_GLOBAL_LOCK_STATUS, 0,
> +                                         ACPI_BITMASK_GLOBAL_LOCK_ENABLE, 0};
> +    const static uint8_t gpe0_mask[4] = {1U << XEN_GPE0_CPUHP_BIT, 0,
> +                                         1U << XEN_GPE0_CPUHP_BIT, 0};

Hmm, funny, in someone else's patch I've recently seen the same.
Can we please stick to the more standard "storage type first"
ordering of declaration elements. After all const modifies the type,
and hence better stays together with it.

And then I'd like to have an explanation (in the commit message)
about the choice of the values for pm1a_mask. Plus you using
uint8_t here is at least odd, considering that this is about registers
consisting of two 16-bit halves. I'm not even certain the spec
permits these to be accessed with other than the specified
granularity.

Or wait - the literal 4-s here look bad too. Perhaps the two should
be combined into a variable of type
typeof(currd->arch.hvm_domain.acpi_io), so values and masks
really match up. Which would still seem to make it desirable for the
parts to be of type uint16_t, if permitted by the spec.

> +    BUILD_BUG_ON((ACPI_PM1A_EVT_BLK_LEN != 4) ||
> +                 (ACPI_GPE0_BLK_LEN_V1 != 4));

Please split these into two, so that one of them triggering uniquely
identifies the offender. There's no code being generated for them,
so it doesn't matter how many there are. Perhaps it might even be
worth moving each into its respective case block below.

> +    ASSERT(!has_acpi_ff(currd));
> +
> +    switch ( port )
> +    {
> +    case ACPI_PM1A_EVT_BLK_ADDRESS_V1 ...
> +         ACPI_PM1A_EVT_BLK_ADDRESS_V1 + ACPI_PM1A_EVT_BLK_LEN - 1:
> +        reg = currd->arch.hvm_domain.acpi_io.pm1a;
> +        mask = pm1a_mask;
> +        break;
> +
> +    case ACPI_GPE0_BLK_ADDRESS_V1 ...
> +         ACPI_GPE0_BLK_ADDRESS_V1 + ACPI_GPE0_BLK_LEN_V1 - 1:
> +        reg = currd->arch.hvm_domain.acpi_io.gpe;
> +        mask = gpe0_mask;
> +        break;
> +
> +    case XEN_ACPI_CPU_MAP ...
> +         XEN_ACPI_CPU_MAP + XEN_ACPI_CPU_MAP_LEN - 1:
> +        is_cpu_map = true;

In order to make more obvious in the code below that reg and mask
can't be NULL, wouldn't it make sense to ditch this variable and
instead use checks of reg against NULL in the code further down?

> +        break;
> +
> +    default:
> +        return X86EMUL_UNHANDLEABLE;
> +    }
> +
> +    if ( bytes == 0 )
> +        return X86EMUL_OKAY;

Did you find a check like this in any other I/O port handler? It doesn't
seem to make sense to me.

> +    if ( dir == IOREQ_READ )
> +    {
> +        if ( is_cpu_map )
> +        {
> +            unsigned int first_byte = port - XEN_ACPI_CPU_MAP;
> +
> +            /*
> +             * Clear bits that we are about to read to in case we
> +             * copy fewer than @bytes.
> +             */
> +            *val &= (~((1ULL << (bytes * 8)) - 1)) & 0xffffffff;

*val being of type uint32_t I understand neither the ULL suffix nor
the and-ing. How about

            if ( bytes < 4 )
                *val &= ~0U << (bytes * 8);

?

> +            if ( ((currd->max_vcpus + 7) / 8) > first_byte )
> +            {
> +                memcpy(val, (uint8_t *)currd->avail_vcpus + first_byte,
> +                       min(bytes, ((currd->max_vcpus + 7) / 8) - 
> first_byte));
> +            }

Stray braces.

> +        }
> +        else
> +            memcpy(val, &reg[port & 3], bytes);
> +    }
> +    else
> +    {
> +        unsigned int idx = port & 3;
> +        unsigned int i;
> +        uint8_t *ptr;

const

> +        if ( is_cpu_map )
> +            /*
> +             * CPU map is only read by DSDT's PRSC method and should never
> +             * be written by a guest.
> +             */
> +            return X86EMUL_UNHANDLEABLE;
> +
> +        ptr = (uint8_t *)val;
> +        for ( i = 0; i < bytes; i++, idx++ )
> +        {
> +            if ( idx < 2 ) /* status, write 1 to clear. */
> +                reg[idx] &= ~(mask[i] & ptr[i]);
> +            else           /* enable */
> +                reg[idx] |= (mask[i] & ptr[i]);

Don't you mean mask[idx] in both cases?

Jan

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